Thanks, confirmed solved.

Ihor Radchenko <yantar92@gmail.com> writes:

"Christopher M. Miles" <numbchild@gmail.com> writes:

I applied your patch on the latest pulled org-mode source code. Still can't org-fill elements quickly when region select text contains org headlines, properties drawer etc.

If I only fill paragraph, it is fine.

Thanks for the pointer. I now managed to reproduce the problem. It was an infinite loop in org–backward-paragraph-once. Fixed on main via cc3df3af2.

Best, Ihor