Like many others on this forum, I have been struggling with my Nest Cameras dropping off line multiple times per day. The problem happened with my old Netar R7000, and continued to occur with the Deco M9 once I set it up.  I took all of the normal steps, even locating a Deco in the garage closest to the outdoor camears with no luck. Finally, two weeks ago I set up a 2.4 ghz only guest network on the Deco and joined the cameras. This seemed to help a lot, but I was still getting periodic disconnects, perhaps 2-3 a day instead of 8-10 from each camera. Lastly, I applied the new beta firmware and switched my network to AES security. I am pleased to say that I have had no disconnects since switching to AES. I don't know if I could now move the devices back to make network, but since everything seems happy I will leave them on the guest 2.4 with AES.

Jon