Thanks a lot for your efforts - I really start to feel guilty now.
I mean not guilty enough to stop you from expanding your kit and solving my problems ;-)...
I just don't know if I could assist you any further because my knowledge about collisions is very small.
In the meantime I've moved most of your graph from the Character_BP to my PlayerController_BP. Btw. I've found a new solution to stop movement it's the UE4 ignoremovement function which puts a status on the character that ... well, makes the character movement to get ignored and is stackable.