I'm using Ubuntu 16.04 and I installed a KDevelop 4.x version via apt-get install. But normally I prefer to use the newest AppImage version. When I need to debug my codes, I cannot insert a breakpoint in the AppImage platform while I can insert breakpoints in the KDevelop 4.x platform by left click on the mouse. Can someone provide some clues? How should I fix that? I have tried to delete my old AppImage and downloaded a new one. However, nothing changes.

Are you sure that the breakpoint is not there?

With certain configurations it is hard to see:
* with a dark theme, and depending on your monitor, the line colour of a line with breakpoint might be almost the same as the background
* check whether the icon border is there (settings -> configure kdevelop -> editor -> appearance -> borders -> show icon border should be on)

I had a similar problem:
viewtopic.php?f=218&t=160753

adamc wrote:Are you sure that the breakpoint is not there?

With certain configurations it is hard to see:
* with a dark theme, and depending on your monitor, the line colour of a line with breakpoint might be almost the same as the background
* check whether the icon border is there (settings -> configure kdevelop -> editor -> appearance -> borders -> show icon border should be on)

I had a similar problem:
viewtopic.php?f=218&t=160753

Thanks! After activating the icon border option, the problem is solved.