Hello, @pootler. If you’re experiencing odd occurrences while using Brave, you are absolutely correct that the best approach is to reduce the number of variables as much as possible. Please note that if you’re on 1.18.75 or later, are using macOS, and have not yet granted Brave access to its Brave Safe Storage, that too could cause access-issues for passwords and more.
Our team also recently authored a guide on how to create a new profile for more successful troubleshooting, you can read it here: Create a new profile to help Troubleshoot. If there is anything I can do to assist you during this process, please do not hesitate to reach out.