Sounds like my situation.
I personally gave up, bought a SONOFF Zigbee 3.0 USB Dongle Plus and switched to zigbee2mqtt.
It’s been a couple of days now and it seems to be doing allright.
Ill try shutting down breakers during the weekend to see how it reacts.
Thanks. It might really just be a IKEA Repeater issue. And somehow only occurring when shutting down the breakers. Just unplugging and re-plugging a repeater still allows them to reconnect (as far as I remember). I know that does not make much sense. I will try to investigate and share my results in here.
I first replaced the IKEA repeaters with SONOFF Zigbee 3.0 USB Dongle Plus (flashed as routers) but still the same problem, Xiaomi devices drop off the mesh and hardly reconnect.
I did not bother to find out whether that’s a Conbee II or ZHA (or combo of both) issue.
I also replaced the coordinator with SONOFF dongle and for a more seamless migration moved to Z2M at the same time. (This allowed to re-pair device by device on the Z2M mesh, while some were still running on ZHA)
After everything was moved to Z2M, none of the issue reoccurred. 
1 Like