Ok gonna say from the top of my head what it is...first for the NPC being on top of the floor or ceiling, could be a fault of not setting the correct X,Y,Z values if you were editing a specific map. The Y coordinate will need to be rounded in order for it to be touching the floor, I do not bother with the 1.38 just round it to 1 that's it. To fix this I would just get a new map file and replacing the messed up one.
And for the DC on a mob, you need another client that matches the EP you are running. If you are running an EP4 client then using an EP5 will only cause issues. You can use the search function on here to find the appropriate client.