Can not save any fields on the profile

In one of our deployment, we cannot save any field of the profiles. There is no setting preventing this, and there is no error. Neither while saving nor in the logs. It appears as saved, but after a page refresh it shows the change actually got ignored.

All fields seem to be hit. bio_raw, title, …

What happens in the network tabs of your browser’s developers tools when you click on Save Changes button? Is there any error in the console tab?

no error there as well. the network tab shows also the request gets send successfully and returns a 200 without any error. but after a reload it just shows the backend never saved the information. The lack of any error messages is which brought me here, any idea where I can look else or what could get a hint of what is going wrong.

There was a similar issue here (with a solution). Perhaps it will give some clues.