having an esp32 with two temperature sensors, also running the webserver on the esp. Did work the past four months like a charm. Since the last updates (ha, esphome) I often see:
But actually it is working fine!
How to fix?
Thanks
Jerry
But actually it is working fine!
Often or only? Did you check the breaking changes before doing the update?
Check how the entities are named in HA (developer tools) 
or navigate to the device page to find them 
Hi,
its an intermittend problem. Some time it says “entity not available” and sometimes it works. On the same day!
But upgrading firmware from esphome works, connecting to the esp32 web server works,…
So then check your status and wifi signal for that node to exclude any infrastructure problems at first:
Hi,
thanks, added the sensors and will kepp an eye on it. However, esp is in the same location since 4 months, showing this problems only in the last days,…
Sometimes AP and Client stay at the same positions still things can move in between. I remember a neighbor changing/upgrading windows and afterwords many wifi devices became unstable as a result. Even small objects (e.g. made out of metal) can obstruct a wifi connection easily if it is in the line-of-sight 
Would be a good idea to share the YAML code of the device. 
Do you have by any chance some bluetooth thingies running on that ESP?