I either get this issue:

"We couldn't save your comment. It might be empty or have invalid formatting. If you copy-pasted, try removing the formatting and adding it directly in the editor"
OR

"We couldn't save your attachment. Reload the issue then try adding it again"
-> I have been attaching the same PNG files for the past 13 weeks, then suddenly it stops for my user and another's.
-> I can comment on tickets and attach the file. But then gets stuck, or displays this:
"Failed to load. Retry"
I have:
- cleared cookies
- cleared cache
- tested on another user on a MacBook
- Ensured the file type is below 10 MB (its 56 KB)
- Used Mozilla Firefox and Google Chrome
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Does anyone know the answer?
Thanks.
Update 1: Also, all existing attachments show "Failed to load. Retry" as well, as seen below:
