Reading this post made me realize that I had not yet tried encrypting the updated S6 Edge Oreo build and therefore didn’t mention it in my testing results.
It is now done, and I have to announce that, sadly, attempting to encrypt the phone results in a bootloop. I was able to get rid of it with a clean flash of the same Oreo build, and the phone is now back to normal.
Moral of the story : do not encrypt this Oreo test build. I’ll update my testing results post to warn others.