Hello.
I've encountered some strange behaviour in late SoA and ToB on Insane - creatures don't use offensive spells/abilities. Spellcasters stick to summons/protection/invisibility/attacks. Mind flayers, beholders, demons simply attack.
This behaviour changed at some point throughout the game and affects not all, but majority of enemies. For example, mind flayers in Underdark used crushing and magical damage abilities, but in Alkathla (in chapter 6) and WK(between SoA and ToB) they try to stay invisible most of the time and attack, if detected.
Or demons: Pit Fiends in WK shoot fireballs or casted Swarms, but they don't use any abilities besides melee attacks further down the road.
Another example is Odamaron: starting contingency with Mordekainens'/Hakeshaars, then Planetar, then Gates/Cacofiends, intertwined with PfMW.
BG2EE 2.6.6.0 on Linux (using ciopfs).
Installation order: Portraits Portraits Everywhere > ASCENSION > UB > ALTERNATIVES > LANTHORN > WHEELS > SCS (v. 34.3).