When using USB receiver mouse, mouse CLICKS sporadically stop working.
Mouse movement is being tracked by pointer without disruptions; even “libinput debug-events” registers clicks,
but they have zero effect on KDE windows and panels. It happens sporadically. At most what I found is that if I log in without USB receiver and attach it later after log-in, movements and clicks work for some time. But sooner or later the problem with clicks will reappear.
On dual-boot Windows, I have zero such problems, so it is not about hardware.