Can't create pull request from forked repo and All commits original repo are gone

Hi team,

I created a forked repo (F) from an original repo (O). Everything working fine for days when suddenly I noticed that I can't view commits in repo O (even that the source codes in repo O still there - please see attached picture for detail).
Then I couldn't create pull requests from repo F to repo O. It said:
"Something went wrong while creating your pull request.
We couldn't load the diff
If you'd like to continue, you can still create the pull request without seeing the diff."

Please help resolve as it really urgent to my team.
Thanks.

Loi