@yohelp it’s hard to say as I have no idea what you might have done. Most people claiming that their passwords or other data disappeared had lost this info during an update. Windows 7 hasn’t been supported for a long time, so yours wouldn’t have been done in an update.
Passwords are encrypted using the OS keychain. If you messed that up (such as resetting your device or anything to damage/corrupt/delete your OS user info), then your passwords would no longer be visible.
Also not sure if you ran a program on your computer, such as Avast Cleaner or CCleaner, which could have erased the data. Or if you might have done a Clear browser data where you had Passwords chosen. The list kind of goes on.
You can always check out NOTICE: Unexplained Data Loss Issue but I think overall the answer is not much can be done for you. Especially since you’re using an outdated and unsupported OS and version of Brave.
Guess last thing I’ll do is tag in @Mattches just to see if he has any further details. But think is kind of limited, especially since you have given so little information.