Hi!
1 - my hubitat c8 has gone off the rails the last 2 weeks. It totally jerked out on zigbee and its only reading about 8 out of 32 devices, and even then it only talks to them on and off. Something majorly wrong has happened. Its been very disappointing.
2 - Australian provider Smart Guys are totally unresponsive for warranty requests on their email line. Not a very reliable reseller.
Are you using the OEM power supply or a poe splitter?
Shut down the hub, pull power for 1 minute and power back up.
Thanks for your feedback. Based on the details you've shared, it sounds more likely that you have one or more misbehaving devices connected to the hub. If it was an issue with your hub's radio, no devices would be working. Have you screened the logs page for any errors and warnings? If you'd like to share more details about the problem you are having, we may be able to help you regain the reliability that you desire.
What devices (make and model) have you connected? Do you have enough repeaters in your system? Have you updated or upgraded your router recently and the 2.4ghz band may interfere with your Zigbee radio?
Oem supply
Have done power cycle, and also tried radio rebuild a few times (both seperately)
No errors or warnings in log it seems.
Radio graph currently shows 16/32 devices attached, about half are not talking when i try to manually switch on or off.
Always had an orbi mesh router network, running 2.4ghz guest and dual band primary network.
Setup is hubitat running api into home assist, both connected direct into satellite.
Not running a zigbee mesh, but I understand hardwired devices supposedly act as repeaters?
Devices are approximately:
2 x ikea auto blinds
15 x nu zigbee light switches
2 x nu zigbee gpos
3 x samsung motion sensors
2 x samsung door sensors
3 x sonoff motion sensors
Light switches and hubitat were setup simultaneously in November last year and system ran like a dream. A few devices fell off over time but nothing that crippled the remainder quite like this.
Thanks for prompt replies, apologies for my frustration, we spent a considerable amount gettimg the light switches setup and then when moving over from smart things, i had to abandon all my ikea motion sensors.
To minimize radio interference issues: On the router 2.4 GHz WiFi should be set to channels 1, 6, or 11 with 20 MHz width. Make sure to turn off any channel ‘optimization’. On Hubitat the Zigbee radio should be set to channels 15, 20, or 25.
Give this a try ..
1st.
You Need to check your WIFI settings and zigbee channel.
Setup your WIFI system to channel ( 1 ) on all routers and AP's and reboot router and AP's.
2nd
make sure / setup hub ZigBee to channel 20 with 8-12 power.
then power off the hub .. using the GUI - Settings / shut down for 3-15 min
3rd
once you have all that setup .. power up hub.
Will take some time for system to settle down and devices to re-join.
4th
You may have a bad / weird USB power brick / supply.
IF you can find / have a different one that is 2+ amps I would try a replace it with the old one!
5th
If you install this program / app it will help find your devices and sometimes
helps them re-join system, also will show what devices are and are not working.
If that all fails ask [ bobbyD ) to look at the system. Good Luck 
Download the Hubitat app
