Forge of the Phoenix not awarding Maven witnessing for party members

I ran Forge of the Phoenix with 2 Accounts in a group, but only one character (the one who opened the map) got the Maven witness completion.

This seems to happen only on Forge (other Formed Invitations maps are working), regardless of wheter the 2nd char is at the start of the map, right in front of the boss area or inside it. Dead or alive doesnt matter either.

Screenshots were taken after porting back to my hideout: