Don't know if anyone noticed, but if you have items equipped from different level of difficulties before you join a game with a lower level of difficulty that item by default will stay equipped on you unless you switch weapons in the box.
So as an example
Someone who has guns on the highest level of difficulty can go into the lowest difficulty game with his OP guns, and basically go through it no problem as long as he doesn't change weapons.
Should be fixed and your welcome nonSENSE