Ok, hears the deal, you maybe running into a bandwidth limit on the COVR with having more than 20 devices connected to the COVR. That many device then trying to connect and maintain 6 additional cameras that are using medium to high bandwidth depending upon video quality your using is probably driving the COVR past it's limits in regards to how many wireless devices and bandwidth it can handle. You would need to disconnect or turn OFF ALL other devices from the COVR router, then connect say 3 to start, cameras to the COVR router and see if the problem continues or not. Generally most home class routers can only handle from 20 est active wireless connections at a time, any more then that you need to off load connections using other APs like your ONHUB using it as a wireless AP, LAN to LAN.
I for one have 3 cameras and 3 NEST Thermostats connected to my COVR system, however total devices would be around 10-15, all others are wired LAN devices.
If the problem continues with just the 3 and 6 cameras connected to the COVR system, then I presume there could be an issue between the COVR system and NEST cameras that need to be reviewed by both parties. I saw this issue couple of years ago with a different router Mfr and NEST Thermostats.
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