There is a chance that your passwords are still there somewhere.
Applications have persistent state (e.g. passwords) stored in a certain way, in SQLite databases, text files, JSON files, whatever. As development progresses, the structure of this data or how it's stored may need to change slightly in newer versions. It is therefore important that the developer makes sure that, upon the user running a newer version of the app for the first time, the existing persistent state is updated properly to a format that is understood by the newer version of the app. If this is not done correctly, the end user might experience "data loss", just like you did.
I said "data loss" in quotation marks, because the data doesn't necessarily have to be gone, just not recognized by the newer version of the browser. There is a chance that your passwords are still stored in the browser profile folder. I do not know where it is on Android systems. But if you find it, and find out how Chromium (what Vanidium is based on) stores passwords, you might be able to find and extract the passwords.