I tried a new power supply, and tried putting a little fan blowing on it too (just because). Still locked up, so it looks like my hub just is defective. In my case I don't think it has anything to do with the software side of thing / resource leaks.
Thanks @bobbyD for taking a look.
Have you never noticed how hot the connect's get on the top? I would not recommend the hub to go on top of it in any orientation.
I hear you and great suggestion!!
Yeah it's not on there anymore but still upside down - this particular Connect I don't use that often so like now for example it's only lukewarm.
Interesting that the hub behavior was very similar to what people have been reporting about slowdowns and lockups though.
My C-4 that just died basically just stopped booting up.. Once in about 15-20 power cycles the hub tools app on port 8081 starts but thats it. Hard resets, firmware rollbacks, soft resets.. Its a hardware issue unfortunately.
I get the same, very occasionally, with my c4 hub too. It will work fine for months, then just won't boot at all.
Since V2.1.6.x my C5 hub has been totally unreliable, have had to reboot every night at 4:00am and quite often have had to reboot 1 sometimes 2 times during the day to keep it working.
Until about 7 days ago i removed the HSM as i wasn't really using it, i noticed a real improvement in the performance of the hub in the evenings, so i after a couple of days i removed the nightly reboot and we are now at 5 days since i rebooted my hub and its still running great.
coincidence ?
Not sure, but at the moment, i'm back as it was with 2.1.5.x
So a happy user again 
Just wondering if you mentioned this support? It could be a good data point for them to have.
No havenāt contacted support directly, I guess since no one else commented then no one else has seen a connection to the hsm, so itās probably a coincidence or an extreme edge case.
Also sort of thought that hopefully they are reading these posts so if they start to see a pattern they will investigate anyway
I would not be surprised, if we went through all the posts about what App or Driver was disabled, greater than 90% of them would be tarred. I believe this is due to the resource issue being at a low, common level. Something that most things use.
sendEvent()
log.debug
Some element that is common to just about everything. (Just to be clear, I do NOT think either of those is a problem, just trying to show an example.)
Said another way, I think we (the community) may be weary of identifying and trying to assist with identifying the problem to Hubitat. Perhaps that's why responses to "yet another App..." are so thin. 
Worse of course, is it being a hardware issue. C-4 vs C-5. Which means the C-7 is the answer? LOL For me, my three C-4's are my workhorses. My pair of C-5's are lightly used, reset all the time and don't retain a config for very long. There's all the proof I need, right? 
What's a C5? 
Same. My C-5 is much slower than my C-4, even though the C-4 has the dangerous apps/devices/integrations.
If I perform a reboot at the same time on both hubs, the C-4 is much faster, although to be fair, it has less devices/rules - just the dangerous/risky ones. The same is evidenced with navigating to the device page.
Unfortunately I only have 2 c5's.
As a result, of the slowdowns, I'm trying to split the workload.
Hubconnect is a great idea and a great piece of code. It's a brilliant idea that the speed of an Ethernet connection could be close to the speed of a zwave\zigbee connection.
Will it all work and eliminate slowdowns?
Stay tuned... Too early to tell.
After solving my overheating issue my one production "controller" C5 now runs great!!! Of course it has both Z-Wave and Zigbee shut off and is only running Alexa and HubConnect with a few virtual devices and rules...but still.. 
I have been having some slowness and reboots (rootin tootin app) on my production C4's from time to time especially on the main floor one but some of that is likely been caused by misbehaving devices and such.
The remaining 2 C5 hubs - one is still in the box and the other is a demo kit I put together which is currently offline and sitting in a plastic bin in the basement.
Can't wait to load up on C7's 
Itās relieving to see others observing the C-5s being slower than the C-4s. Until my server hub failed a couple weeks ago Iāve been using C-4 hubs for the server and 2/3 remotes.
I replaced the server with my C-5 dev hub and itās been considerably slower. It also seems to suffer the hub slowdown issue much quicker than the old C-4.
Itās noticeable enough that Iām considering swapping my C-4 dev hub back in.
I'll chime in. My C5 is slower than both my C4s. It also has some mild corruption that spits a random SQL error once every few days. I've been unable to fix the corruption, so I might end up swapping it with a C4 anyway.
My C5 runs pretty well. I've had issues, who hasn't? But they've been mostly self inflicted. I can't say I'm using only stock drivers and apps, because I'm not. I do only have the one hub, maybe that's a useful data point? I'm on my 3rd one, I've had a bad run with lightning strikes, just one of the perks of Florida living. So I'm sure I'll see a C7 soon enough. Well I've shared enough, time to walk my pet gator and make sure the palmetto bugs don't steal my hurricane kit.
I have a single C4 sitting in the corner of my cool basement so heat shouldn't be a factor. It runs a heck of a lot of stuff and I've had no issues with it. I wonder how much temperature is a factor as well.
Yeah I screwed up by putting the C5 on top of a SONOS Connect which by itself gets warm but the top is also very smooth and heat reflective. Once I flipped it over and moved it off have not had those kinds of issues since so I'm fairly confident that was a factor.
In terms of regular use - like others I am hesitant to add a bunch of devices to the C5 but it seems to work well as a cloud app / master hub controller - I also generally keep rules affecting local devices local to each hub. I already had the C4's and really like the flexibility of the removable zw/zb usb stick (single nortek stick for U.S.). If the C4's are faster I cannot tell from my current setup but they are not any slower (except on certain occasions) and are doing more "work".
Hardware-wise are the C4's actually better?
Just wanted to bring this to your attention, in case you hadn't already seen it.
Download the Hubitat app
