I have recently replaced some failing devices and got everything back up and running. However, an old problem has reappeared over the last few days. Every evening multiple devices drop off and become unavailable. I turned off my hub last night and restarted it. Most devices came back slowly but a couple didn’t return until this morning.
I have one wifi extender. Hub located next to router. All devices that drop off are smartthings – multi, motion and water
It sounds suspiciously like interference between 2.4GHz WiFi and Zigbee. If you haven’t come across that before the bottom line is that Zigbee and 2.4GHz WiFi channels have a considerable overlap. Your hub will have a fixed Zigbee channel (I believe selected from a range when first used) so you are stuck with that but you can force the WiFi to use a channel that keeps as far out of its way as it can rather than using an automatic selection which might choose the worst one (and may vary when you reboot your router).
Ideally you want to minimise 2.4GHz WiFi use, especially with boosters, and get some distance between the hub and the router. Ten feet is often suggested but any distance is better than nothing. Using mains powered Zigbee devices to provide repeating to strengthen the Zigbee mesh can help too.
There are several discussions on this subject on this community and many more on the net to give you more info.
It might not be that at all, but enough boxes have been ticked for it to be considered.
With regard to WiFi, I think it’s really a case of making a point of using 5GHz if you have it and your devices support it. If you don’t have it there isn’t a lot that you can do.