Mysterious graphic that makes ubuntu host unusable

[reader]

Setup:
  Hardware: HP xw8600 2x xeon 56?? - 32 GB ram
Running: ubuntu 20.10 with zfs on root

Trying to describe a phenomena I see every so often.  I have not been
able to isolate the culprit.  It just is not apparent what things have
to happen to cause this problem.

Some times when I have left the machine running and switched over to
a windows host thru a KVM switch connecting two servers

When I switch back to ubuntu zfs I sometimes find a full screen graphic
displayed.  No amount of twiggling the keyboard will get thru and show
the hosts lxde desktop. Not spc, or backspc, or esc, or
control-alt-del.  Or any other keyboard press or combo I could imagine
will get thru the the desktop.  There is no prompt asking for creds.

I can logon thru ssh from the windows host and do everything in text
mode that one would normally do.

I've searched thru ps wwaux output for anything to do with locking or
screen or the like.  I killed a few pids but so far have not hit the
right one.

There are 550+ pids showing...  So I really have no idea what I'm looking
for.

Some kind of screen locking seems most likely but I have definitely
turned off the screensaver in desktop selections, so it does not even
start on bootup/login

I figured I could find a pid for X and kill that but I do not see such
a thing... maybe overlooking it.  Probably overkill but I'm really at
a loss as to what to do to trace down the program doing this.

I've been getting restarted by first going in thru ssh and shutting
down 2 VBox vms I often have running thru VBoxManage at cli.  Once
that is done in a way that no harm is done I then reboot that server.
Quite a tedious pita what you are working hard on something

I know there are things that are designed to lock out all but the
current user.  And one is required to reinsert there login creds to
get to work.

`ps wwaux|grep lock'  turns up about 10-12 pids of the format:

  `... [kworker/0:0H-kblockd]' (sq brackets not added).  Which seem
  unrelated.

This grahpic that takes over the screen does not offer any kind of
UID passwd type thing... it offers nothing and responds to nothing
I've found so far.

The problem does not happen every time I leave the host running and do
something else... just occasionally . . .

Can anyone guess what program would put up a graphic that effectively
locks the OS from use thru any normal means

Any suggestions would be greatly appreciated.