Hello,
i have done as many of you some testing. It just finished 3 side quest (possession, cabaret and carnal sin). I get 2*50xp in cabaret 0 for all the rest. And took about 1 hour for the tree of them. I checked some youtube video on 80% of them, no xp gain at the end (so i assume people still play even with the bug). On some, i saw 750 xp received for possession. Our main problem here is to define if we lost any xp or not. I can off course still enjoy the game. But for many players getting a reward for a quest is a motivation (for some a very strong). Don't forget that after many quests, you received just some coins ans the xp no supra power weapon or stuff.
I don't get too the comments posted by the dev about : " even with the lost xp you will still be in the range expected". For the main quest surely i have no doubt as even without investing any point for some levels i can still make any quest higher then my level easily. But for many people, part of the fun is to have the strongest Gerald of the world.. And making them loosing 5-6 level at the end just break this fun part. I hope they will fix it soon, so far i stop playing and wait for the patch.
So I've been going along fine the past week, and had not run into this XP bug. Then last night happened. Finally got to Skellige. Accidentally queued the Echoes in the Dark main quest looking for the place of power. Got through the first half of that mission (mandatory), and received XP. But I loaded a manual save, circumvented the main quest and got the ability point from the PoP. I didn't want to start the quest yet because I wanted to get all the PoP around Skellige first so I could reset my skill points.
So I set off to find the last 3 or so, and the last island I went to had the side quest "Possession" so I said what the hell and decided to compete it. Pretty sure I received XP in the middle of the quest, but when I went back the second time (its a two part quest) and completed it successfully I received no XP.
I knew then I was hit by the bug but I wanted to test it out.
I went back to the Echoes in the Dark mission. This time, after the first part I received no XP (even though I did receive XP the first time). Then I went onto complete the quest and again, received no XP.
Thankfully I have a manual save after getting all the PoP around Skellige. Tonight I'll load it up, completely skip the Possession side quest, and go straight to Echoes in the Dark. Who knows if I'll get XP for it but its worth a try. Also worth noting I was Level 19 and the side quest is Level 17.
Also, I did the same thing Yakyak did and pulled up both quests on Youtube. One video showed a user also not receiving XP for Echoes in the Dark or Possession. While another user did receive XP for both quests.
Its strange how this bug is triggered at different points in the game for people. I'm not sure if the Possession side quest was the trigger in my case, or if its just luck of the draw. I will report back tonight/tomorrow.