The double xp booster effect is not being applied to end-of-level xp or to crew bonuses.
Beginning xp: 209,611
Confirm that double xp booster is activated:
Do Papa yeti dungeon solo so I can take screenshots without being interupted:
Kill boss. Xp before opening the end-of-dungeon chest is now: 209,661
Open chest and loot. Xp is now 209,711
Receive a completion bonus of +125 and a crew bonus of +45
Close the screen and check the tavern to see if xp is being “secretly” added and that it might just be a display bug. See that it isn’t, and my xp total is still 209,881
209,711 + 125 + 45 = 209,881
The double xp is NOT working. Also note that the old +10% boosters gave a visible popup during the post-dungeon-tally and showed the xp bonus incrementing in bold. The new boosters are not doing that either.