Probably your API login token is time limited, and therefore it expires after X days.
It’s quite common practice I think.
I have tado myself, the expiration happens (estimated) once in 9 to 12 months.
You’ll have to request for a token check at the app developer I guess. I’m sure they “forgot” (meaning: too much work for a small customer fixable 2 time a year issue)
Unfortunately there’s more silent errors @ Homey…
Did the flow get ‘broken’? Did the tado device cards have a ! sign on them?
If so, you can use Flow Checker to detect that and you’ll have a workaround.
