Thank you for the reply John. It got me thinking, and it turns out the block editor comments were just leftovers from testing the new editor experience before switching to the old and copying some content over to other fields. I assumed these comments were incorrectly being added to all WYSIWYG fields, but it was just me.
Good to know, false alarm, topic solved.
Welcome to the Advanced Custom Fields community forum.
Browse through ideas, snippets of code, questions and answers between fellow ACF users