Polaric Invitation didn't drop

Since I'm pretty sure Singular Focus does not apply to Invitations (at least it didn't since it was introduced) something else seems to have prevented my Invitation to drop.

I just killed the 14th Map Boss in the rotation (it was Defiled Cathedral) but the Invitation didn't drop at all. After realizing I was past the 14th Map clear I even went back to double check if my (now stricter than before) Loot Filter just didn't show it but even after forcing loot to show and changing / deactivating the Filter, nothing dropped at the feet of the Boss.

I don't know what could've caused this but I thought it would be worth a mention since I personally can't see any reason why that would've happened.


Kind regards.