The only time(s) I've seen a proper Rema failure was due to the the puncture being larger than a couple of mms, and the patch eventually began to aneuryism/rupture. I stated in another thread where I'd "doubled" over a patch. This is when I did such, sucessfully. It's now SOP this type of puncture.

Mind y'all, Ccyco's admonition. For this reason I don't "grate." Besides, doing so scores the tube.
Who desires that?
Chemical buffer for me, or scraping+spit with a razor then alcohol cleanse if I puncture a 3rd time--which does happen...
...Or come-up with a thought-to-be-repaired spare that won't hold air *but only a little*

Remas (by me) have failed, due to operator error. This is why I have come to prefer them: they can be removed--carefully-- and another placed saving the tube for another ride series.

I do though let the patch "cure" for as long as possible. Usually more than a day (if I'm fortunate some weeks....).

Lastly, when in doubt, double down a second coat of glue. Might help, can't hurt.