Root password does not work after restart

Hello, since some updates, we had the same problem, every time we restart, root password is changed and not working anymore (for ssh or screen login, not web).

When I set up SSH keys, I still can access it, thanks, and so if I reset the root password, it works, and I can login successfully... until I restart again.

I just downloaded and install a fresh install, but the same problem occurs. So I can't really work with this situation, too risky... Why is this happening ?

Thanks