PLUM-XBOX-BUS

I played vita for about 40 hours. When I opened everything I wanted on Vita, I decided to synchronize the saves with the PS4 version. However, it is impossible to do this: the game on PS4 does not see the save from the vita. What could be wrong?

Its last weapon for me. I was farming it about 40 hours on 51 and 54 missions, but this gun havent dropped. So can this weapon be obtained on this missions? I think that I can farming weapons on 59 mission, but it can get more time.

Can I play coop with 4 other players?

I know that all other EDF games have 6-9/10 difficulty and can take 200+ hours, but this game haven't UR trophies, is this easy quick complete?