Same issue as this one:
Authentication error (Code: 10000) in profile and
API Request Failed: POST /api/v4/user/tokens (500) when trying to create API-Tokens.
Tried different browsers on different locations, log-in & -out, private mode → no improvement
Seems to be a more or less common issue, as there is a significant number of similar tickets - without solution besides posting a ticket, though.
Any suggestions how to proceed?