Jiquani´s Machinarium Coop Bug

Good day,
a friend of mine and myself are playing together and reached Jiquani´s Machinarium. We found out that you can not use any small soule core when playing together. You have to leave bevor you pick up the first one. And you could only rejoin after the first door was unlocked. We tried everything (rejoining after picking up direktly, Both graping one and even trying to put it in at the same time) nothing worked.

i hope i could help any of you and maybe help fixing it.

Marry Christmas and a Happy New Year.