It would be really helpful to know how you finally solved the problem.
I am experiencing a similar (or the same?) problem where I have a vault in my Dropbox which can’t be opened by the Cryptomator app. The connection to Dropbox seems fine but it keeps telling me “wrong password”. I also tried it with a vault on Google Drive but with the same result.
Opening the same vaults on my Windows PC works absolutely fine.
I am using v1.3.2 of the app with Android 5.1.1 along with a software firewall (NetGuard) where I made exceptions for Dropbox and Cryptomator.
EDIT: I tested creating a new vault in my Dropbox with the Android app and it worked fine. The vault can be opened and filled as normal. But If i try to open this vault on my desktop PC it also tells me “wrong password”. So it seems my problem works in both directions. Is this a matter of encryption which is done different on PC and phone?