Since another thread has addressed the issue of earning a loot box through Role Queue/Quick Play which they couldn’t open, and the solution has been found, I’ll open a new thread for the subsequent problem that seems to be causing.
Any loot box earned during an event has always been an event box, regardless of what mode or method it was earned through. Earning a loot box through QP role selection during an event should produce an event box. I can only imagine that it must be a bug, hence I’m posting here and not elsewhere. I’m having this issue on PS4, so I can’t provide any diagnostics unfortunately.