When you return MoM foundables the game is not registering your XP for the Brilliant Event Part 2.
Probably a stupid question, but just making sure you’re account that it’s the MoM family XP and not wizarding XP, yes?
I’m having the same issue. A MoM foundables that gets me, for example, 100 xp, will only give me 3 xp credit towards the goal. And that’s WITH baruffio’s
There's a difference between wizard xp (used to level up) and family xp (used to increase your rank in a particular family).
I borrowed this image from @MacOdeatH because it gives a good illustration of what you're looking for: