Update: I tried creating a new style after disabling each add on, to try and pinpoint if one was causing it.
After reaching the end of the list of add ons and creating 20 new test Styles with no parents (None of which worked when tested), now the first 10 Styles are working properly.
Is there a background task that creates the template files and I'm getting blocked on I/O or something?
Update 2: I went to the Rebuild Caches section of the admin panel and there were unfinished processes waiting. Running that caused all missing template files to be generated. Weird that adding a style doesn't seem to prompt if creating a new style doesn't fully complete all necessary work like other functions do