Are you positive? You have an XP boost active along with the bonus ones from the forge pass? This would be highly irregular, unlikely. Will need to see a screenshot and/or video of this in action, for sure.

Also, double check you're in the right difficulty relative to the XP you think you should get.

i first notice it i got the 10% FP banner, no other banners. my level 1's only made it to level5. with the normal xp banner they made it to level 6. Party comp 2x 60 and 2x 1 level. the battle is on brutal 12-3. I will have to wait a couple of day for my XP banner to fall off. i will post the results here.

And to be clear, you did purchase the Forge Pass (and earned enough XP to get to the 10% XP boosts), correct?