Thought I'd give #Zigbee one last try and... it works. Turns out that all the problems I had before were caused by a dodgy/cheap/crap USB Zigbee dongle. Trying a new configuration with a Sonoff dongle and all the repeaters, gadgets and gizmos I've bought to play with over the last few years suddenly work!
@kravemir I can't remember what it was - I seem to remember it was a device that had to be programmed, but it was a while ago. The problem was intermittent connectivity, loss of devices, poor signal etc. etc. Nothing I could say "this is definitively the problem" - it was just flaky and unreliable.
@NAB I'm bit curious, because I've currently got #Aeotec Zi-Stick (ZGA008), and things are flaky sometimes.
Map in #zigbee2mqtt shows some battery powered devices as not linked to any router - floating.
If I add an extra router, and have at least 1 router per 6 end devices, then all works good.
Wondering, if I would need less routers by switching coordinator to #Sonoff ZBDongle-E. It claims max 32 direct children.
I don't have a poor signal, though. Only the issue with number of end devices.