There are changes like these mentioned in the changelog: "Also in Order of the Virtuous Blood, if the player sides with Seridur, he will be made non-essential after the quest, as he is involved in no other quests"
Similiar to the ticket here
https://afktrack.afkmods.com/index.php?a=issues&i=36683 NPCs being essential for seemingly no reason seems to not be considered a bug by Unofficial Patch Team standards. There are other examples like this in the UOP and SI and DLC Patch. I suggest looking for the term essential in the changelog to find all the cases.