There’s several threads on the forum looking at Zigbee issues, however they tend to be for more unusual or specific issues.
I find IKEA TRÅDFRI switches (UK 240V) work well as Zigbee mesh repeaters, although I’d suggest enabling firmware updates in ZHA in case that is an issue. Updated firmware certainly fixed my issues with the 5-button remote.
My own setup moved from the Sonoff USB radio with a great aerial to a Yellow with only a PCB antenna, so has always included powered Zigbee devices in the same room to ensure the best mesh possible.
If this helps, 
this post!