The usual causes for an instance to shutdown unexpectidely (or a not responding instance) is either:
- an “out of memory” or a “stack overflow” or an infinite loop somewhere in the custom code
- a misconfiguration like a unrelevant circular reference which may result in an infinite loop in the platform’s code
It seems that your instance has been corrupted (see last answer by @Francois in this post: Undo changes - Link - #9 by david) this may also result in unexpected/unpredicatble behaviors.
In this post I proposed to restore a backup or to reset the instance, I think it is the only reasonable approach if the platform system configuration is actually corrupted. Just tell me which option you prefer = restore one of the last 7 days backup or completely reset the instance