As a bit of background - I'm playing the GoG.com version of NWN - Diamond on a Mac through Wineskin, so I don't have access to the toolkit. Which could be part of the issue.
I've only just started playing the original campaign, and after rerolling a second character noticed that it was receiving MUCH less XP from kills than my first character. My first character made it to level 5 before I rerolled, and when I started playing Chapter 1 with the second character, I noticed it was receiving anywhere from 1/2 to 1/5 of the XP my first character was. Mobs from the Prison Break quest were giving less XP per kill at level 3 than the goblins in the prologue. By the time my character was level 4, they were giving only 7 XP each.
I rerolled a second character simultaneous to this, and it was dealing with the same issue at level 3 until I reached level 4, and then it started getting more XP per kill from the same mobs at level 4 than it did during the previous level - as if issues resolved on level-up. I ended up deleting both characters and rerolling again, and the same severely reduced XP issue happened again.
None of these characters were multiclassed outside of racial restrictions, and none of them were playing with henchmen/minions, so there's effectively nothing in-game that would cause a drop in XP, let alone an ~80% reduction in XP from kills. Quest XP seems unaffected. I'm wondering if this has to do with the challenge level registering improperly, since it almost seems like my version of the game is treating my character's challenge level as twice what it actually is.
Does anyone have experience with bugs like this, or any idea of a potential workaround? This could effectively making the game unplayable, since my character will always be far behind how strong/leveled it should be going forward. If there exists a mad genius whose sole purpose (for some reason) was to mess with CRPG players, this is more or less the exact thing they'd put in motion.
Any potential leads or solutions would be greatly appreciated, since entering Chapter Two at level 5 (if that) might be a fate worse than death.