Can't find any invites/event letters ingame.
I've been playing many matches since the event started and so far I only was able to find 8 of those. Now I see there's a mission which requires to find three of those things just to proceed on the tome and yet I can't find a single friggin letter/invite.
How much luck do you even need to find those? There really need to be some changes, they should have a distinct aura which should be visible from greater distances.