Sorry, I don’t know if using mqtt will help. I use service calls in HA to control almost all attributes of wled integration and I have not had any issues yet, aside from the interference issue.
Haven’t tried mqtt yet. I will probably do so soon though as I cannot set secondary or tertiary colors, or toggle either mirror effect or preset cycle/playlist via service calls. I know secondary and tertiary colors can be controlled using mqtt but I’m not sure about mirror effect and preset cycle/playlist. When I do try mqtt though I will try and see whether there is a difference.
Regarding the Wifi, my connection to wled device is not particularly great but it still works without issue.
Even the sync function between wled devices works correctly and they both have a fairly weak signal.
Your wemos d1 mini is very close to router so the cause shouldn’t be a bad Wifi connection. So maybe the problem is something completely different. Have you checked the HA log for any error messages after seeing the unexpected behavior? If there are that may give a clue as to what the issue is. Maybe try removing and re-adding the wled device on integrations page. Could be the DHCP on your router keeps issuing different IP addresses to the device for some reason. You can set a static IP in wled web ui. Or, if you prefer, set a reserved address for the device on the router itself.
Also you can take a look here if all else fails: FAQ · Aircoookie/WLED Wiki · GitHub