Ajax call throwing a 200 for a user, a 302 for another

A user just called and said that a function was not working.
I tested it in the end, everything worked.
Set up a screen sharing and noticed that she was getting an answer 302.
When we opened the request URL in a new tab, the expected data was returned.

See attachment 232358

So, both under Windows, same browser, same function, same input data

What would cause this suddenly?