The rares correct name is "Sabriel the Bonecleaver", but it shows as "Sabreil the Bonecleaver" on the clicktarget frame

https://www.wowhead.com/npc=168147/sabriel-the-bonecleaver

I tried manually changing it in \WTF\Account\<My Account>\SavedVariables\SilverDragon.lua, as that seemed to be the only place the name was stored, but it keeps reverting to the misspelled name.

Amusingly, this one is because Blizzard had it misspelled for the initial launch of Shadowlands and it's wound up stuck in caches for ages. (Note that it's still misspelled in the achievement, for instance...) It's supposed to pick up changes when you're near a mob, but it's fairly possible that the precise codepath is getting blocked somehow.

Anyway, the reason it's reverting is probably if you're changing the savedvariables while WoW is still running. Whenever you reload/logout it saves whatever's currently in memory, overwriting any changes you've made. If you completely quit WoW and change it, it should stick.

I'm going to do some speculative testing of how well things work without that localized name cache nowadays. It used to be really necessary, but that was years ago and how Blizzard handles caching of mob data has changed a lot since then...

Okay, the alpha resulting from that latter commit should fix the issue for you next time you're close enough to target Sabriel. I'm going to leave this ticket open to track that I'm looking at the general cache issue.

It has indeed been fixed!