Act 3 - Oswald not available

Playing on couch co-op mode makes the vendor disappear from town. When you enter the town in solo mode, Oswald is there for P1, not there for P2 even in solo. This is an issue as the Molten Vault quest drops an item that needs to be delivered but can't be done so if the vendor is not there, and for P2, even in solo he will never be there.

is there a way to solve this?