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