I'm logging all errors/warnings/notices and none of them is related to that process, would have been too easy.
Already done everything on the link you provided, that's how I made the conversion work.
The issue can be reproduced on any document, even a blank docx.
Something interesting though, if I exit before the quit(), then the response is very fast and the conversion works fine, but the word.application process is still running in the task manager.
Without the exit, I can see the word.application closing after the 30sec.
If I set a 10sec time limit, the script still takes 30sec and crashes (error 500).
Using Windows Server 2022, Office LTSC Professional Plus 2021, PHP 8.0.28 (nts-Win32-vs16-x64) and Phpdocx 14.5 premium.
I'm starting to think of an asynchronous way to do it ..