Works flawlessly in Windows, but Android app won't show vault files

Downloaded and paid for Android app. When a vault is opened it says that the vault is empty, yet looking at it in Windows says otherwise. I suspect that I am missing something, but all I get when opening a vault is greyed-out note to “select masterkey file.” The vault is located in Dropbox, which says that I am logged in.

I am moving away from Boxcryptor, which worked just fine in Android and with Dropbox. I can’t help but think that I am missing something obvious, but can’t figure out what it is. I downloaded the user manual and have been through it several times but cannot find my error.

Hi. Can you please confirm that the sync between your PC and Dropbox is fully done and all (encrypted) vault files are online in your Dropbox?

It appears to be so. Works great in Windows. Checked sync history from within Dropbox in Windows and it shows the most recent as today.