Okay, I see what happened now.
The proper way to create customized stylesheets in 8.0 is to change or create a custom.sty file in the project. During the migration to 8.0, Paratext examines the stylesheet used by a project and compares it to usfm.sty. Any differences that are found are put into a new custom.sty file inside the project. It then changes the stylesheet of the project to be usfm.sty (custom.sty overrides the settings in usfm.sty). This seems to have worked just fine for your project.
However, 4 days ago, an administrator changed the project back to using the old stylesheet from PT7 - usfm_indppa.sty - (he must have put it into his My Paratext 8 Projects folder). However, stylesheet files outside of projects are no longer S/R’d in 8.0, so when the changed settings got to the other users, they got a “missing file” error.
To fix this issue, an administrator must change the stylesheet back to usfm.sty and then do a S/R. Any user already affected may have to copy the usfm_indppa.sty file, temporarily, so they are able to do a S/R to get the fixed settings.
In the future, any wanted changes to the stylesheet should be done by changing the custom.sty file in the project.