I experienced the same issue, I tried to launch plymouth manually from an X session:
~$ sudo ./plymouth start
the screen becomes black (with a message at the top about /dev/sda), it is not possible to interact at all. CTRL-F2 to switch to a console, ps -ef does not show any plymouth service, however and I tried to stop it:
~$ sudo ./plymouth stop
a message confirmed it has been successfully stopped (!), however the graphical session remains freezed.
I experienced the same issue, I tried to launch plymouth manually from an X session:
~$ sudo ./plymouth start
the screen becomes black (with a message at the top about /dev/sda), it is not possible to interact at all. CTRL-F2 to switch to a console, ps -ef does not show any plymouth service, however and I tried to stop it:
~$ sudo ./plymouth stop
a message confirmed it has been successfully stopped (!), however the graphical session remains freezed.
~$ reboot
and since then the problem is gone.