Exact same problem (at the unlock screen, it is not possible to enter any characters on the password box, as if focus is not there) on Xubuntu 18.04 and Xubuntu 20.04 in three different machines (two laptops and one desktop); problem existed since 18.04 and persists after upgrade to 20.20 focal fossa.
Exact same problem (at the unlock screen, it is not possible to enter any characters on the password box, as if focus is not there) on Xubuntu 18.04 and Xubuntu 20.04 in three different machines (two laptops and one desktop); problem existed since 18.04 and persists after upgrade to 20.20 focal fossa.