I have four (4) Brave Release Version 1.47.171 profiles. I could not open any of them this morning. I opened Beta 1.48.132 and Nightly 1.49.49 (updated after opening) without any issues. I only have default profiles in Beta and Nightly. I rebooted my computer and problem was resolved.
I was using all instances of Brave off and on all day yesterday with no problems. I closed all instances of Brave once finished.
Yesterday, I was mainly trying to clean up bookmarks across instances and was moving, copying, pasting, and deleting a lot of bookmarks mostly in the two profiles with the most bookmarks. I did turn on Sync for at least two profiles and then removed the profiles from Sync chain. I closed Beta after I cleaned up the bookmarks there. I don’t have a lot of bookmarks in Nightly but I did have it up continuously for playing background music.
Just thought I would post as I thought this was really strange. Take care.