I have installed Parrot Security version, update and upgrade these days.
I have a repeated problem: when I want to open, for example, file properties (in Mate), system signout to graphical login.
Same thing when I run a long command in Terminal: the system kill all apps and signout.
But not in all the cases, just apparentely with no logic.
Can you help me with an advice, a solution?
Thanks
That is weird, how did you update your system?
Using apt-get update?
sudo apt update
Your system can be broken 
It is recomended always use:
parrot-upgrade
instead of apt-get update/upgrade
i never had saw this problem.