Bug#929834: Also seeing it with gdm3
On a Dell Latitude with Intel graphics, running gnome flashback, I also
saw this behavior after upgrading from stretch to buster. This laptop,
however, is running gdm3, not lightdm. I am seeing the exact same
symptoms, with VT switching generally working around the issue
So far, the workaround at
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=929834#66 has resolved
this for me. I will update this bug if I see any further issues.