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Do a local backup (download the backup) then restore right away (which automatically does a soft reset in the process). There is a chance you are encountering a rapid memory decline, which that will fix.
It is very odd that you can ping the hub but not connect to the diagnostic tool. I have never heard of that. Usually if the diag tool wont come up the hub is dead to the world and wont respond to anything. You are trying to access the diag tool on port 8081? Hubitat Diagnostic Tool | Hubitat Documentation
