F.Y.I. Had this error also for several month and managed to solve it today…
- Check your entities for doubled names.
- In case you find doubles - dig deeper
For 1 - I used hints from…
I guess the simplest solution is described here …
I did it the hard way I extracted a backup of my home assistant system
Folder not 100% sure
homeassistant\data.storage\core.config_entries
File 100% sure
core.config_entries
…and used the yaml to table converter described here…
To get my data into MSExcel … There I used the “find doubles function” from Excel to identify my fritzbox (router) to be the one with 2 entries with the same name
For 2 - I googled the Fritzbox Integration of Home Assistant… found out, that Fritzbox Tools was moved into the HA Core at some time… disabled one of the Fritzbox Devices and voila… Overview Page is now working (Ctrl + F5 in your Browser if it is not working directly)
Hope that helps… I posted my solution because I googled my problem and found this thread to be one of the first answers…