No longer a problem for me.

Operating System: KDE neon 5.23
KDE Plasma Version: 5.23.3
KDE Frameworks Version: 5.88.0
Qt Version: 5.15.3
Kernel Version: 5.11.0-40-generic (64-bit)
Graphics Platform: X11
Processors: 2 × AMD A6-6400K APU with Radeon(tm) HD Graphics
Memory: 7.7 GiB of RAM
Graphics Processor: AMD CEDAR

Freshly installed:
Operating System: Fedora Linux 35
KDE Plasma Version: 5.23.3
KDE Frameworks Version: 5.88.0
Qt Version: 5.15.2
Kernel Version: 5.15.4-201.fc35.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 8 × Intel® Core™ i5-8265U CPU @ 1.60GHz
Memory: 23.3 GiB of RAM
Graphics Processor: Mesa Intel® UHD Graphics 620

Don't have any problems with it, but I'm using this one https://github.com/dfaust/plasma-applet-netspeed-widget. I did have to install ksysguard ( if I recall correctly) though for it to work.

marcinko wrote:After a year, the bug has not been fixed, the widget does not work and also eats up all available memory (24GB) in a second

Still not working as of May 2023...