WOW! 400 tabs is an incredibly high number of tabs (I rarely have more than five or six open at a time and never more than a dozen)) and expecting any browser to retain so many tabs between sessions is unreasonable. Instead of trying to retain so many tabs, have you considered bookmarking the site on each tab? That way, you would have less onscreen clutter and you would always have access to all the websites you go to. Also, you can backup and restore bookmarks.
Brave can easily handle hundreds of bookmarks. I have so many, I categorize them in folders.