In case somebody else will be looking for a solution, I had the same issue:
After shutting down the server to create a clone, Mariadb didn't work anymore after the restart of the server and Wordpress obviously wasn't able to connect to the database.
What fixed the issue in my case was updating WordOps with:
and then doing a restart:
wo stack restart
Hope this help somebody.
To be honest I find it very worrying, that a simple restart of the server without having any changes applied in the recent weeks brings the stack resp Wordpress down.