Ah, great, well I’m glad that Grammarly have figured the cause of the issue at least and are working on a fix. I thought it might turn out to be links, and the reason I asked you to check TextEdit is because if the problem occurs there then it rules out a specific problem with Scrivener (if TextEdit had worked, then there would probably be an extra factor in Scrivener that was involved).
Fingers crossed Grammarly are able to fix it fairly soon.
All the best,
Keith