Glad it helped a bit!
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Written in install order.
I am a short way away from Nashkel in Chapter 1. Finishing up in Beregost/Friendly Arm. Experimented with removing all party members and turning in some final quests to get main PC to level 2 because I wanted to see if it would result in everyone else reaching 2 as well due to Improved NPC's Customization, to confirm everything was in working order.
I installed SCS's "improved npc customization component" but it only seems to work for Imoen, Neera, Garrick and Kagain so far, the level up component that is. Montaron, Xzar, Khalid and Jaheira do not level up when re-added to party, they get no XP added to them whatsoever. Seeing that Neera needed to be re-added twice to reach level 2, I thought I would try removing and re-adding the rest who had issues but it didn't work, not even if I added them alone.
I noticed I erroneously added ToB style NPC's from Anthology so I removed that but that hasn't fixed the issue, although I tried it on the same save game. Could this be caused by the Anthology tweak that allows one NPC from NPC pairs to be re-added after removal? Load order looks fine to me so I don't think its that.
Any ideas?