Login error - Customer API: Request failed with status code 502

Suddenly on 1 of my tenants (development tangent) I stated having failed logins.
On Monitoring > logs I can see “Faild login”:
and inside the description shows:
"error": { "message": "Request to Webtask exceeded allowed execution time", "oauthError": "access_denied", "type": "oauth-authorization" },
Digging a bit more:
I used the extantion Real-time Webtask Logs:
There I can see:
Error calling Customer API: Request failed with status code 502

I didn’t find any similar case online. But then I’ve found that another user is logged in successfully.
The difference between the users was in the user_metadata. the user with the successful login had additional metadata field:
"customer": "<html><meta http-equiv=\"refresh\" content=\"0;/.well-known/captcha/?r=%2Fapi%2Fcustomers%2F\"></meta></head></html>"

On the users that failed to login this field wasn’t present. This field was not created by us.
What is the meaning of this? Why suddenly it appeared and why do we need it.
On other tenants, we don’t have this field and everything works just fine.

Thanks a lot!