yeah this happened to me too >.< was fighting a fortification for 10 minutes as 75SAM/DNC. and got 15 xp, 7 allied notes...
hopefully they'll fix that. it looks like they made xp based on damage. but since fortifications barely take any damage..... you barely get any xp when hitting them :P
just before i did maybe 15 minutes in the jungle fighting orcs. and got 650ish xp, and maybe 500 allied notes.