Co-op play and level progression issues

There are 2 different bugs I'm experiencing. With co-op play the level of the 2nd or more players are different after switching back from co-op play. Those players experience and huge disadvantage with the mobs vs the weapons used to kill those mobs. They can not defeat those mobs on their on-line games to progress through the game. The second bug deals with the weapon scaling vs the soul Regen in their hotbar. Is the soul regen supposed to fill when hitting the mobs or when killing them? Are then any know issues like I'm experiencing with my friends playing vs when they switch back to their own games? I tried reading the known issues and didn't see anything mention theses I'm seeing.