Thanks for the direct link to that page, anon468618; it just takes minutes to load here… If someone could compile a PDF of 3.0, it would be most welcome! Or do I understand from your comment that it is “so new that you may need Paratext 8.1” that USFM 2.4 is valid for PT8? Well, in any case, a PDF would be great for offline reference!
Anyway, it looks like \rem is still valid in SUFM 3.0, so it must be a bug. I’ll try reporting it.