Observed this one 2 separate cases, one Xubuntu 18.04 -> 20.04 installation where light-locker caused it and on a fresh Lubuntu 20.04, that was converted to XFCE, where xscreensaver was the issue. Also had 3 other Xubuntu installations that went from 18.04 to 20.04 and did not encounter these issues.
Observed this one 2 separate cases, one Xubuntu 18.04 -> 20.04 installation where light-locker caused it and on a fresh Lubuntu 20.04, that was converted to XFCE, where xscreensaver was the issue. Also had 3 other Xubuntu installations that went from 18.04 to 20.04 and did not encounter these issues.