Same here, it’s unusable on Ubuntu 18.04.3 LTS (does not happen on Windows using the same extensions and config).
Brave ver: Version 0.68.141 Chromium: 77.0.3865.90 (Official Build) (64-bit)
Edit: Disabling Sync as per Browser crashing after being opened after 10-30 seconds every time it is launched seems to work for now.