I bought 3 APs and it looks that my house is too small for 3 - as I can not return them, I need a bigger house.
Had all 3 setup as zero handshake. That sets all of them on to channel 1 (and 36 for 5GHz), with no option to change it.
When looking at signal strength for channel 1 in several places in the house all 3 APs are present on with roughly the same signal strength (~ -55dBm). That is probably not good...
Changed one of the 2 GHZ AP to fixed channel 11 HIGH power output and removed it from zero handover and moving the others a little bit to better cover the range
Then put some non movable devices (2 cameras and 2rPi) onto channel 11 on that AP. Now it seems to run much better.
The 5 GHz channels do not have that problem as their range is much smaller.
Also my son has a chromecast that sets up its own wifi signal on channel 1 - its gone now. That helped too.
The ping time for wireless devices are now 1-50 msec and only rarely > 200msec. It naturally depends on the siganl/noise ratio at that position.
Just in case you run into that kind of problem
Karl