I'm having some problems getting the XFCE Power Manager to lock using physlock. When I set the Lock Screen on Lid Close action, upon opening my laptop lid I'm presented with an alternate lock screen, and after entering my password I get the error None of the screen lock tools ran successfully, the screen will not be locked.
However when I manually run xflock4 from a terminal emulator, physlock is correctly used.
The relevant xfconf LockCommand setting is thus:
➜ ~ xfconf-query -c xfce4-session -p /general/LockCommand -v
physlock
And my power manager settings are this:
physlock was correctly working in the past using these settings, but as this stopped working some months ago, I'm afraid I won't be much help in narrowing down what triggered the initial change.