The case and full name of the authenticated user as defined in AD is shown in the message "No user exists with SNC name". This message shows that the user has been authenticated and their SNC name is shown in this message. The SAP user is then determined by the entry in USRACL table and there needs to be an exact match.
I asked you to change, save, change again and save because there is a field in USRACL for each entry (like a checksum) which is generated when you save the entry, and I have seen an issue before where the checksum is not valid anymore so saving the entry again causes the new checksum to be generated. As you have tried this, it looks like the issue is something else.
If you have checked the name is correct and the case is correct, then I cannot think of anything else which might be wrong. Maybe you can share the screen capture showing the message you see when you try to login and also showing a screen of what the SNC tab looks like in SU01 for the user.