I encountered the same issue today. (Haven't been to the fighting pits yet, haven't used any magic in the game yet either beside teleportation scrolls.)
Could mods I installed for Skyrim/Skyrim SE affect Enderal if I never added them for this game, and don't see them to in the Data Files section of the launch screen? (No mods, attached a screenshot)
I see SkyUI is active within the game... though I remember that needed to be installed differently than others, and is tied to SKSE.
Paycrimegold 0,0
and
resetAI
didn't prevent him from becoming hostile.
(I can't do a resetAI on him after he attacks, as he is not "targetable" from then on.)
I've attached a save, it is from before entering the area where the drummer is located (Undercity Barracks).