So, I, as usual start Krita.
I create a new file, but as soon as I touch the tablet with the pen, krita just crashes
Does anyone know what is the cause of this crash?

Kubuntu 19.04
Intel Celeron N3060
4gb Ram
Intel HD 400

Terminal output:
Application: Krita (krita), signal: Aborted
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[Current thread is 1 (Thread 0x7ff931e81800 (LWP 24888))]

Thread 8 (Thread 0x7ff9121aa700 (LWP 24991)):
#0 futex_reltimed_wait_cancelable (private=<optimized out>, reltime=0x7ff9121a9c10, expected=0, futex_word=0x7ff904003c50) at ../sysdeps/unix/sysv/linux/futex-internal.h:142
#1 __pthread_cond_wait_common (abstime=0x7ff9121a9cc0, mutex=0x7ff904003c00, cond=0x7ff904003c28) at pthread_cond_wait.c:533
#2 __pthread_cond_timedwait (cond=0x7ff904003c28, mutex=0x7ff904003c00, abstime=0x7ff9121a9cc0) at pthread_cond_wait.c:667
#3 0x00007ff937e696b5 in QWaitCondition::wait(QMutex*, QDeadlineTimer) () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#4 0x00007ff937e697e6 in QWaitCondition::wait(QMutex*, unsigned long) () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#5 0x00007ff937e66de1 in ?? () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#6 0x00007ff937e63612 in ?? () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#7 0x00007ff935c85182 in start_thread (arg=<optimized out>) at pthread_create.c:486
#8 0x00007ff937adcb1f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 7 (Thread 0x7ff9119a9700 (LWP 24990)):
#0 futex_reltimed_wait_cancelable (private=<optimized out>, reltime=0x7ff9119a8c10, expected=0, futex_word=0x560f1b5aa430) at ../sysdeps/unix/sysv/linux/futex-internal.h:142
#1 __pthread_cond_wait_common (abstime=0x7ff9119a8cc0, mutex=0x560f1b5aa3e0, cond=0x560f1b5aa408) at pthread_cond_wait.c:533
#2 __pthread_cond_timedwait (cond=0x560f1b5aa408, mutex=0x560f1b5aa3e0, abstime=0x7ff9119a8cc0) at pthread_cond_wait.c:667
#3 0x00007ff937e696b5 in QWaitCondition::wait(QMutex*, QDeadlineTimer) () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#4 0x00007ff937e697e6 in QWaitCondition::wait(QMutex*, unsigned long) () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#5 0x00007ff937e66de1 in ?? () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#6 0x00007ff937e63612 in ?? () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#7 0x00007ff935c85182 in start_thread (arg=<optimized out>) at pthread_create.c:486
#8 0x00007ff937adcb1f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 6 (Thread 0x7ff9136ef700 (LWP 24948)):
#0 __GI___libc_read (nbytes=16, buf=0x7ff9136eeb40, fd=19) at ../sysdeps/unix/sysv/linux/read.c:26
#1 __GI___libc_read (fd=19, buf=0x7ff9136eeb40, nbytes=16) at ../sysdeps/unix/sysv/linux/read.c:24
#2 0x00007ff9355024d0 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#3 0x00007ff9354bb78f in g_main_context_check () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#4 0x00007ff9354bbc60 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#5 0x00007ff9354bbddc in g_main_context_iteration () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#6 0x00007ff93806c063 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#7 0x00007ff9380175bb in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#8 0x00007ff937e622c6 in QThread::exec() () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#9 0x00007ff92b6a2376 in ?? () from /lib/x86_64-linux-gnu/libQt5Quick.so.5
#10 0x00007ff937e63612 in ?? () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#11 0x00007ff935c85182 in start_thread (arg=<optimized out>) at pthread_create.c:486
#12 0x00007ff937adcb1f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 5 (Thread 0x7ff91b2ec700 (LWP 24947)):
#0 0x00007ff937ad0729 in __GI___poll (fds=0x7ff90c004e30, nfds=1, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
#1 0x00007ff9354bbcb6 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#2 0x00007ff9354bbddc in g_main_context_iteration () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#3 0x00007ff93806c063 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#4 0x00007ff9380175bb in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#5 0x00007ff937e622c6 in QThread::exec() () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#6 0x00007ff92b3d2ef5 in ?? () from /lib/x86_64-linux-gnu/libQt5Qml.so.5
#7 0x00007ff937e63612 in ?? () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#8 0x00007ff935c85182 in start_thread (arg=<optimized out>) at pthread_create.c:486
#9 0x00007ff937adcb1f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 4 (Thread 0x7ff91aaeb700 (LWP 24946)):
#0 syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
#1 0x00007ff937e65c30 in ?? () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#2 0x00007ff937e65aa2 in QSemaphore::tryAcquire(int, int) () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#3 0x00007ff936c69ada in KisTileDataSwapper::run() () from /lib/x86_64-linux-gnu/libkritaimage.so.17
#4 0x00007ff937e63612 in ?? () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#5 0x00007ff935c85182 in start_thread (arg=<optimized out>) at pthread_create.c:486
#6 0x00007ff937adcb1f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 3 (Thread 0x7ff922f3a700 (LWP 24891)):
#0 0x00007ff937ad0729 in __GI___poll (fds=0x7ff91c01d170, nfds=1, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
#1 0x00007ff9354bbcb6 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#2 0x00007ff9354bbddc in g_main_context_iteration () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#3 0x00007ff93806c063 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#4 0x00007ff9380175bb in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#5 0x00007ff937e622c6 in QThread::exec() () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#6 0x00007ff935cb3565 in ?? () from /lib/x86_64-linux-gnu/libQt5DBus.so.5
#7 0x00007ff937e63612 in ?? () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#8 0x00007ff935c85182 in start_thread (arg=<optimized out>) at pthread_create.c:486
#9 0x00007ff937adcb1f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 2 (Thread 0x7ff929361700 (LWP 24890)):
#0 futex_wait_cancelable (private=<optimized out>, expected=0, futex_word=0x560f13125768) at ../sysdeps/unix/sysv/linux/futex-internal.h:88
#1 __pthread_cond_wait_common (abstime=0x0, mutex=0x560f13125718, cond=0x560f13125740) at pthread_cond_wait.c:502
#2 __pthread_cond_wait (cond=0x560f13125740, mutex=0x560f13125718) at pthread_cond_wait.c:655
#3 0x00007ff92995e36b in ?? () from /usr/lib/x86_64-linux-gnu/dri/i965_dri.so
#4 0x00007ff92995e0d7 in ?? () from /usr/lib/x86_64-linux-gnu/dri/i965_dri.so
#5 0x00007ff935c85182 in start_thread (arg=<optimized out>) at pthread_create.c:486
#6 0x00007ff937adcb1f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 1 (Thread 0x7ff931e81800 (LWP 24888)):
[KCrash Handler]
#6 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
#7 0x00007ff9379e4535 in __GI_abort () at abort.c:79
#8 0x00007ff937a4b726 in __libc_message (action=action@entry=do_abort, fmt=fmt@entry=0x7ff937b71952 "%s\n") at ../sysdeps/posix/libc_fatal.c:181
#9 0x00007ff937a5259a in malloc_printerr (str=str@entry=0x7ff937b735e0 "free(): double free detected in tcache 2") at malloc.c:5352
#10 0x00007ff937a546d5 in _int_free (av=0x7ff92c000020, p=0x7ff92c0025a0, have_lock=<optimized out>) at malloc.c:4209
#11 0x00007ff9383fe2d0 in QTabletEvent::~QTabletEvent() () from /lib/x86_64-linux-gnu/libQt5Gui.so.5
#12 0x00007ff93a0213c7 in ?? () from /lib/x86_64-linux-gnu/libkritaui.so.17
#13 0x00007ff93a01b035 in ?? () from /lib/x86_64-linux-gnu/libkritaui.so.17
#14 0x00007ff93a01b394 in ?? () from /lib/x86_64-linux-gnu/libkritaui.so.17
#15 0x00007ff93a01f049 in ?? () from /lib/x86_64-linux-gnu/libkritaui.so.17
#16 0x00007ff93a022728 in KisXi2EventFilter::nativeEventFilter(QByteArray const&, void*, long*) () from /lib/x86_64-linux-gnu/libkritaui.so.17
#17 0x00007ff93801644f in QAbstractEventDispatcher::filterNativeEvent(QByteArray const&, void*, long*) () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#18 0x00007ff931769580 in QXcbConnection::handleXcbEvent(xcb_generic_event_t*) () from /lib/x86_64-linux-gnu/libQt5XcbQpa.so.5
#19 0x00007ff93176a50d in QXcbConnection::processXcbEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /lib/x86_64-linux-gnu/libQt5XcbQpa.so.5
#20 0x00007ff931794673 in ?? () from /lib/x86_64-linux-gnu/libQt5XcbQpa.so.5
#21 0x00007ff9354bbaae in g_main_context_dispatch () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#22 0x00007ff9354bbd48 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#23 0x00007ff9354bbddc in g_main_context_iteration () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#24 0x00007ff93806c047 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#25 0x00007ff9380175bb in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#26 0x00007ff93801f5e2 in QCoreApplication::exec() () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#27 0x0000560f11d9a937 in main ()
[Inferior 1 (process 24888) detached]

I had the same issue with the install from "discover" on kubuntu 19.04 but when I downloaded the appimage and used it, all was good.

Yes, we know the cause of this crash: a bug in Qt. We reported the bug to the Qt project, but it hasn't been fixed yet. We've worked around it in Krita 4.1.8, which apparently Kubuntu hasn't packaged, and in Krita 4.2.x, ditto.