I have 2 M9 plus, both connected to the router via network cable, both in AP mode, DHCP comes from router. Internet connection is fiber 1Gbps.

Every few minutes, the wifi connection on the main deco will drop and immediately reconnect. The led on the Deco remains green. The second deco does not seem to drop connections at all.

I have this issue since upgrading to firmware 1.6.3

I tried replacing the M9 with a spare, but the same thing happens.

Both iPads have same iOS version (most recent). 
I already tried completely restarting the iPads and the Deco's.

Also tried forget network and reconnect with password.

internet connection itself does not break, wired connections continue to work without issue.

I turned off beamforming to no avail.

fast roaming was never on.

Another odd feature: all iOS devices get named 'iRobot Corporation' as soon as the i7 vacuum connects to wifi.

Also: only iOS devices seem to be affected. My work computer with very connection-sensitive VPN does not seem to disconnect.

network scan executed and optimization as well, didn't help.

I also have a different network with an X20 (on the same router) in the house next door. No issues reported there (but no iOS devices there either).