Hi Keegan Bear,
I'm here to help with your problem.
Does this happen every time? If the read-only user closes the file, can another user write to it?
Also, try again to see if other users can write to the file if the read-only user has the other file open.
If this happens only with the file and not with other files, then this file may be broken...?
If you have any questions, feel free to ask.
Best regards,
Yu