Hello,
I lost all my saved passwords (luckily I had a backup). So when I re-imported it, everytime after closing the tab with the saved passwords, they would disappear.
I looked for a solution and thanks to this post https://community.brave.com/t/my-autofill-passwords-have-disappeared-how-do-i-get-them-back/433367/7 I realized I had changed my Windows account’s password. So I removed Login data files from
C:\Users[username]\AppData\Local\BraveSoftware\Brave-Browser\User Data\Default
and imported passwords again and they stayed! I’m using the latest Brave Beta. I’m writing this for other users as well as for hopefully a bugfix, as I it may happen again and I might not have a backup.