It isn't incompatible, you just don't get xp from some monsters, if you add mods that aren't fully compatible/integrated with it.
Prove it. :blink:
As mentioned before this simply isn't right. Latter versions of OXP use scripted tokens which get dynamically added to all monsters in the cell, modded or no, and then calculate the given amount of xp based on different factors.
If you're using and old version, upgrade, or if you really think your claim is correct, post the conflicting mod. At least this is my understanding of how the script works.
There are only two relatively noticeable issues with OXP, one of them only affecting users with Supreme Magicka who don't get XP from kills made with elemental shields. This happens because there is
no way at all to detect a kill done in such a manner.
The other issue is a bit more widespread, where kill detection gets borked when killing NPC summoners.
None of them are game-breaking, and considering the feat OXP is, they're honestly not really worth mentioning.
Saying "when will it get fixed" and not telling what needs fixing isn't exactly the best way to go about it.