Check response to disabling quick roaming. The iMac is running a fairly old OS X.

It is disabled. I am currently stable for some reason after entering up address and router address manually on an older iMac. Other devices seem stable as well. Holding my breath! Throughput is...

I’m super frustrated. I’ve got several devices (all Apple) connected to my net run by deco M4s. All have at one time or another connected successfully including to the internet with no problems....