I had the same severe CPU use with low usage. I tried removing devices, apps etc. and am no sure why but tried turning ON my Zigbee and then turning it OFF.
The warning showed my Zigbee off (since I have no ZIgbee devices), but in settings it showed it as ON!?
having cycled the Zigbee enabled/disabled (disabled atm) all good for 48 hours now (never went a day without the warning previously.
Note: using C-5.
Things look quiet right now, load is very low. Ping me if it starts acting up again, I'll check it out.
I have had to work for 11 days straight so haven't had time to fiddle with the C4. The load should be low because there has been no z-wave stick in for at least a week. (At least that should prove that it isn't the heat of the room that was causing the severe CPU since it has been in the same spot for the week just without the zwave stick) Also I have removed every app and basically every add on that is possible. I am going to install the zwave stick and then start deleting and turning off devices. That seems to be the last step.
@sharonhouseauto Interesting suggestion. I have no zigbee devices either so I am trying it now.
Please let me know if/when it misbehaves.
It's been over a week and still good! Pretty sure this fixed the problem for me.
Would guess a bug in Hubitat software that lead to it saying Zigbee was off in the notification but was actually on is the root cause of the problem.
@sharonhouseauto That's great to hear. I hope you are all fixed. I disabled my zigbee radio too.
Here is what I have done since I last posted. I unplugged and turned off all z wave devices. Then I started turning them back on physically and in Hubitat. I have been doing one every other day or so. It was going quite well right up until it wasn't 
I plugged in one GE outdoor receptacle and activated my phone in devices so I could use the app again around the same time. Then I got a severe hub warning. I turned both the GE and my phone back off in hubitat. Then I went into Hubitat and turned off the zwave radio but that did not get the severe warning to stop. So I physically unplugged the Hubitat. It has now been up for 9 hours without the severe warning. I will wait a day or two before trying to reactivate more devices.
@gopher.ny It is still misbehaving
Could you please try turning the phone back on? It's very unlikely that phone handler produces the issue, and we can just exclude it altogether.
Is "Lights Fountain" the GE device you're referring to?
@gopher.ny Ok. I turned the phone on. Yes the "lights fountain" is the correct GE. It is physically unplugged and now deactivated in Hubitat
This is not good for your zwave mesh. Disabled devices are still in the radio’s db. Unplugging a disabled device doesn’t mean the zwave radio will not be trying to route through it.
If you think it is causing issues, you should exclude the device.
@gopher.ny Hi again. I received a notice that there was an update on the Hubitat yesterday. I updated to the latest. It came online 8/3 8:11am. 8/4 6:37 am Severe Hub popped up in the log. All I did on 8/3 was turn on the whole house fan via my phone at approximately 5-7 pm. Then this morning when I woke up at 5:49am I when to the Hubitat app to turn off the fan. The app showed it was off so I didn't click anything. Later in the morning when I walked to the kitchen I heard the fan. It was still on.
@gopher.ny Severe Hub CPU came back again after the last reboot. I think I got 3 days without the error. It is still on and mostly responsive. I have not unplugged it yet.
@aaiyar I fully agree with you, the device should be deleted. However, I am first trying to diagnose Severe Hub CPU. If having a single unplugged device in the zwave mesh causes Severe Hub CPU then I think we might need the engineers to rethink the whole zwave system.
As indicated in my message, I thought you unplugged it because you thought it was responsible for the severe CPU issues (for eg. if it is something like a Zen25).
As opposed to your belief that I suggested unplugging it causes severe CPU issues. Unplugging won't do that - it will still mess with message routing in the z-wave mesh, rendering other devices unresponsive or poorly responsive.
@aaiyar Sir, please accept my apology. I am in no way trying to be difficult or insult anyone. I am sorry if my message came across as aggressive. That is in no way my intent.
I am, however, a bit frustrated because of my situation and that may have come through in my message in the wrong manner. I started having the Severe hub CPU issue early in this year (February or March). Out of frustration, I started this thread in early July. So it has been over a month of diagnosing and over 6 months of issues with no end in sight. I just want my little system to work.
I realize that most of the people on this forum, likely including you, are in no way paid for their time. So I am very appreciative of all the replies that I have received. Please accept my apology.
Nothing stands out as wrong... so I'd say set it up for a nightly reboot to deal with symptoms for now. I had a chance to observe the hub in its "high load" state, and busy bits happened to be in an OS process, which our support tools have limited access to. My best guess is it's trying to use swap space, the symptoms match. But there doesn't seem to be enough going on otherwise to trigger swap. In a nutshell, I don't have a root cause yet. However, a band-aid solution may work just as well, and there's a hub rebooter community app that makes reboot setup a breeze.
Just thought I would bring this to a conclusion. I installed the community app that gopher.ny referenced to reboot the C4 each night. I first tried to have it just restart each night but that failed and I had to have it reboot it each night. That seemed like such a huge bandaid fix that I decided to buy a C7. I removed and then installed all my devices on the C7 and have not had an issue yet.
Let's hope it stays that way.
(anybody want a C4?)
Sure, what will you take?
Florida, 32223
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