MySQL auto restart and “Permission denied” error

I have a remote MySQL server “5.7.34” running on ubuntu18, it acts recently so strange.

At a specific time each day, it goes into shutdown, I have checked crons and events, but nothing there.

When it tries to start again I get this error:

(ERROR) mysqld: File '/var/lib/mysql-files/tmp.SomeNumber' not found (Errcode: 13 - Permission denied)

Then “Aborting” and shut down forever.

I have the correct permissions on this dir “750” and it’s owned by mysql. The tmp files already in dir and have the “rw” permissions for user “mysql”.

Thank you for your help and answer.