I’ve had some issues updating my profile page. It took me some time but here is the root cause I’ve found.
If the UI is not in english (I was in french), then the message to sign is also in french.
The issue is that the backend does not recognise that there is a timestamp and returns a 400 saying that the timestamp is missing.
I guess the fix here is to either force english for the signed message or update the backend to make timestamp identification language agnostic.