I am experiencing repeated issues with my laptop (running current TW, 20200701)
when sitting in the dock with a second monitor connected.

It usually starts with the second monitor going dark, then getting signal again
(and the monitor displays the current input as info, so indeed the signal seems
to have been gone?).  Sometimes, it does stay black until I move the cursor in
there and/or go to a workspace that has a window on that screen.

Sometimes, in that situation where the monitor is black, moving the cursor to
that screen doesn't help, but short after that the whole computer freezes dead.
 It also isn't pingable via network anymore, only 5s power button switchoff
helps.

I've seen it several times already over the last months, sometimes not for a
longer time.  With the current release I had it 2 times already, plus a
coredump of kwin after a restart (the first coredump since many months)

Unfortunately I never found anything in the logfiles after a lockup.  And the
system is configured not to write coredumps, so also nothing from the kwin
crash :(

In short, I don't really have a clue if that is software or hardware, or how to
narrow it down, as I have so far not found a way to produce the issue.
I *think* it is only happening after the monitors went to DPMS suspend, and
with no window on the second monitor.  

Hardware is a Lenovo T460p, Skylake with HD530 graphics, and Xorg based
KDE/Plasma.

Maybe someone has an idea what to check/look for.