It might be a &#%×"> but removing some end devices, and adding some router devices should do the trick.
Then you could try to add those end devices, and your new ones again.
And then pair them, in Robert’s words, at or near their final location.
Athom’s zigbee advice here.
Regarding zigbee channel 11:
wifi channel 1 can still be busy if you have neighbours with wifi whithin wifi range.
You can check it with
- Android tools: Wifi Analyzer (and Wifi Heatmap can also reveal interesting info)
- Iphone tool: Network Analyzer Pro ($4,‐) (and Wifi Sweetspots (=heatmap))
