TypeError when creating Entity

[piegamesde]

Jan 26 01:24:23 hass[21981]: 2022-01-26 01:24:23 ERROR (MainThread) [frontend.js.latest.202112200] http://localhost:8123/local/check-button-card.js:592:60 Uncaught TypeError: Cannot read properties of undefined (reading 'toString')

I created some buttons in the configuration. I get "Entity doesn't exist. Create?". I click the check mark. It then says "NaN days ago" and prints the above error message into the log. After reloading, it is again at "Entity doesn't exist. Create?".

[piegamesde]

Okay I think I found the root cause: I was using sensors.foo.bar as the entity name. The application created a sensors.foo entity instead and then got confused. I changed the name to sensors.foo_bar and now it works fine again.