Wifi 1 and zigbee 11 is def. the worst combination
From reading your findings, I can advice to switch wifi 2.4GHz channel to ch.6
but preferrably to ch.11 as a first step.
Changing the zigbee channel is a bit of last resort, while you possibly have to re- pair an unknown number of devices afterwards.
The neighbors 2.4GHz wifi is most probably on auto-channel, so it can be any channel on another day.
And if it’s a weak signal, it should not really interfere in theory.
About the zigbee channel change warning:
your zigbee mesh can take some time to settle again;
Non-responsive devices can be forced to use the new channel by re- pairing them (do not remove them prior to it). Just pair them, and restart their specific apps afterwards.
