Bug that gives you 89+ xp

Hello!

My friend lets call him MR Anderson went to Red Archer and completed the dungeon. Upon completion he got 89k - 100k Xp
So he replayed the dungeon a few times.
But wait. MR Anderson needed to repair his gear for some reason.. So he left, repaired and went back to do more runs.
But sadly he didn't get the xp "boost/bug" or what that was again.

After a day or so I came online and started playing with him. Lets call me MS Anderson. He told me about this bug but he couldn't get it back.
So we went together and POOF me and him got 89k to 100k xp per run.
But sadly MR and MS Anderson are stupid. After a few runs we got bored and thought we could get more from another dungeon.
We left and said to each other HEY this SUCKS. I wana go back to Red archer.
So we went back and by then we got only 49k xp.

Now we don't know if this was a bug or xp boost from something.

Red Archer
Completed in 5-6 min
MR and MS Anderson were Karok
Only items used is from Battle supplies
Oath of Honor = Win without repairing armor
Mode = Hard

The only thing we could figure out was that If you have the Quest and enters the Instance the first time you will be getting this xp and everyone with you or maybe max up to 2 ppl.

No picture was taken sadly.
Please share your findings on this.