So, I've read about the XP glitch, but fourtnely I haven't experienced it.

BUT now I seem to gain very little small amounts of XP from missions. Did a main mission with recomended level of 10. Then I was level 13. I only gained 5 XP from the mission. Then did a side missions recomended level 10, me level 13, and only got 5 XP.

Is this some kind om bug or something else?

Depends on the mission. Some are kinda pupped. I literally got one pupping xp from one. (I did the pups because I support that move by the forums)

Some parts of missions give you very little XP if that's what you mean. Usually upon completion you get a bigger reward.