There seems to be a bug in UltraEdit Text/Hex Editor (x64) Version 27.10.0.164. So I upgraded to 64-bit UltraEdit 2022.0.0.102.
Reformat now doesn't work at all for a largish file, e.g. 500 lines with right margin set to 999, and only 20 chars on each line.

I cannot reproduce an issue with UltraEdit for Windows v2022.0.0.102 on using the command Reformat Paragraph.

I created quickly a file, see the file Reformat_Paragraph_input.txt in the attached ZIP file. Next I clicked on ribbon tab Format in group Paragraph on command Setup to open the Reformatting Options window. Hanging ident was not checked, Use paragraph left margin was selected with Right margin (after # column) configured to 999 and Alignment was set to Left. I clicked on button Reformat and the last paragraph was reformatted as expected. The caret was at end of the file on opening Reformatting Options window. I set text cursor anywhere in the middle of second paragraph and clicked on ribbon tab on command Reformat and the second paragraph was reformatted too. I pressed Ctrl+Home to move caret to top (= beginning of first paragraph) and clicked once again on command Reformat and the first paragraph was reformatted also as expected. See the file Reformat_Paragraph_output.txt in the attached ZIP file.

Conclusion: The command works.

Please describe more detailed how the command Reformat Paragraph is used by you on which data in which text file (line ending type, character encoding).

Allow me to explain the subject line.

In the course of daily study, I often export lecture/meetings into a video/subtitle folder. No problem with that as I end up with two files, one is the original .mp4 (or sometimes .mp3) and the other file is a .srt - a plain text file.

1. With one of my laptops (Windows 10 Professional), I end up with a .srt file, for example "The lecture on 06-01-22.srt" which has approximately 83,700 characters as a three line file. The first line is a timestamp, something like 00:00:01 - 02:15:01. The second line contains a "monster long" single line of text with all the talking, audio, subtitle, closed captions. Line 3 is blank.
2. Another of my laptops (Windows 11 Professional), using the same download/export, I end up with the same two files, but the .srt text file is neatly broken up into timestamps with line breaks. So instead of three lines, I will have something like 2,100 lines and timestamps above each line of talking, subtitles, closed captions, etc. and each line has less than 80 characters/columns. So no need to reformat.

Now, ordinarily, none of this is a problem as I would simply use "Reformat Paragraph" to wrap the text when using first machine (Windows 10 Professional) and expected to see all of the captured and saved text split up into neat looking lines with columns 1 to 80 (or close to it).

Instead absolutely nothing happened/happens. The 83,700 characters long line does not disappear and the file remains visibly intact without any change.

So, I end up opening the .srt file on first machine (Windows 10 Professional) in either WordPad or MS Word and lo-and-behold, both present the "monster 83,700 characters long single line" neatly broken up into lines, each line being about 80 characters long. I can then use Save As and work on this file, but would prefer not the "need" to use WordPad or MS Word.

Why is UE not doing same when I "Select All" and "Reformat Paragraph"?

Version on both machines is 2022.0.0.102 64-bit

EDIT: I see this has already been reported - will wait for next release / bug fix.