Anyone having this issue, please fully read post by Mattches at NOTICE: Unexplained Data Loss Issue and reply there with as much information as possible.
Brave is investigating and working on getting things resolved. There’s no ETA. It may not be quick. It’s unknown at this time if information will ever be able to be recovered for those who have had it vanish. They are trying to figure out what’s going on with everyone and hoping to get the best solutions. Unfortunately it’s not quick or easy to do.