So it used to be the lower level and the upper level shared the same ID I think? But now they use seperate ID’s for each. I only noticed cause it broke my mount addon and I had to manually add in the new ID to fix it.
…WoW 11.0 - Revenge of Oribos confirmed? 
probably just some weird accidental spaghetti code tangling from a recent hotfix, i’d say
Hmm … is there anything a typical player (not delving into such technicalities and experiencing broken add-ons) would notice being different because of same vs different map ids? Any little quirks?
Oribos getting destroyed by death pirate davy jones tentacle boss and then replaced with Acherus
Not really. Like I said, only noticed it because my addon suddenly decided it didn’t recognize where I was anymore.
Might be a new 10.2.6 theory or two here 
No.
I did not notice.
Because I typically avoid Oribos and the Shadowlands like the plague 