When running Parrot XFCE it appears that two different login screen are installed.
The default Parrot Login (Also used in Parrot Mate) works fine,
but once the password has been entered causes login2 (controlled by XFCE settings) to appear as well.
This second screen does not accept any keyboard input (but is otherwise responsive), making it impossible to log in.
When is the bug observed:
This issue happens when the screensaver activates, causing the password prompt to reappear. It does not happen during login.
How to fix the bug:
It is possible to fix this issue by disabling the second login screen using xfce settings (screensaver tab).
The default password prompt still appears though, ignoring the settings.
You could likely also uninstall one of the screens, though i have not tested that.