Funny you should mention that .. On the PM thread I specifically asked if you still needed access to the C8 - 7 days ago or I was going to need to roll back and got no response to that either .. I finally gave up waiting and rolled back to the C5 4-5 days ago as I need things to work, or I need to know something is happening in the background while I'm inconveniencing my household.
I've offered to coordinate diagnostics, perform tests, anything HE wants me to do ... but in the last 9 days this is the first acknowledgement of anything.
So, lets discuss it here instead so others can weigh in.
Could it be mesh? Sure, however ... Every time I move the mesh to the C5, it takes about 5-10 minutes, everything works, and everything is just as reliable and solid as it's always been. I switch the C8 back in, and the entire system goes down the toilet.
We're not talking about slowness, an occasional miss, or generally frustrating behavior ... the mesh is dead as a door nail from the hub's perspective, and nothing can be commanded for hours at a time or more. I did deal with it for nearly a 5 day stretch at one point (much to my family's chagrin), there was no improvement seen - in fact, I'd venture to say it seemed worse.
The fact that the same mesh, unchanged, works fine on the C5 and not the C8 leans me away from thinking the mesh itself is the problem (maybe in error). I do, however, accept that there may be a difference in the way the 500 series chip vs the 800 series chip interacts with it. In that case though, I don't think any amount of "settling" is going to make a difference, do you? (I also mentioned this in the same PM from 7 days ago where I also mentioned several other possibilities, and suggested two possible approaches to testing)
I'm willing to do pretty much anything you want - besides plug it back in and cross my fingers. As you pointed out, there are a lot of devices connected to my mesh ... and they all have things to do; many of them are only controllable from the hub - so simply leaving the C8 connected in perpetuity is not really an option.
I think we're beyond a "wait and see" approach. Been there, done that ... the problem I see with this theory is that even if it can take days for the routing to optimize, "dead" shouldn't be the result of insufficient routing, and if it was, I'd expect the reverse to be true when reverting to the C5 after days on the C8. That's not the behavior I see.
So besides plug it back in ... do you have any more ideas? The only thought I have at the moment is doing another backup from the C5 and a fresh restore to C8 after a factory reset. However, if you or the community think other tests or diagnostics done on the C8 in its current state could be beneficial, I will leave it intact for the moment.