During the last days I tried to bisect the kernel
source from Github
in order to isolate the point where the effect started (remote
origin: firstname.lastname@example.org:openSUSE/kernel.git). Interestingly, the
effect did not show up until 4.16.0-rc6, while that same desktop PC
already showed the effect during the distro upgrade around 4.15.13
(which was in March).