Forgot to record or take screenies but this just happened earlier. I’m not sure if anyone else has experienced this.
I go on my routine 130 solo-rush: create a party (by myself) and enter the dungeon.
For some reason, I got into the dungeon with another solo-rushing player (who also has his own pre-made party).
What we did (though I can’t confirm if this was what at least fixed any possible issue with cube drops) was that I asked him to leave his party and join mine. When we killed the 2 bosses, each of us did get a cube each time.
I do know of an already existing bug wherein a party member gets thrown into an instance different from the rest of the party.
I can only imagine 10 people full-running a dungeon. The fun and FPS drops. 
