I finally started a new game with some selected mods. BG Unfinished Business, Sirene, Isra, Aura, and SCS. Everything seemed to be going great until I recruited Xzar and Montaron. Specifically, they are REALLY ready to level up. I believe SCS resets their level to 0 to allow you to set up NPC companions the way you want, but the level up button never went away. I had Xzar at level 18 before realizing it was getting silly. (that was the point where non-existent, invalid HLAs appeared). Montaron likewise just kept going and going like the freaking Energizer bunny. Interestingly, Imoen leveled up as expected - once.
I'm assuming this is an SCS problem, and since I *just* started, this would be the time to fix the issue. Any ideas?
UPDATE: It gets weirder. I reloaded from a save game and now Xzar levels correctly, but Montaron still doesn't.
Also, since I forgot, this is BGEE 18.104.22.168. I deleted and redownloaded, so this is a fresh install (less the override folder)
UPDATE2: Apparently something is resetting their XP to cause them to continuously level up. I can fix the issue by resetting it myself with the console. I will have to see if the problem crops up when they level naturally.