I have had a few instances of Mango running for a couple of years now.
Two running 1.12.4 and two with 1.13.0.

Just recently I have been unable to save changes made to an existing data source or even create a new one on both 1.12.4 versions and on one of the 1.13.0 versions.

I am not even able to activate or deactivate any either.

There are no message in logs to give any indication of anything wrong. I have restarted the instances several times but this made no difference.

Any help appreciated.