@Alleycat crashing was a bit of an issue at the end of last week. We had two possible solutions that seemed to resolve it for most. Can you check them out below and see if either fixes it for you?
Also for another, it was:
Beyond that, what will be needed is for you to go to brave://crashes and see if you have anything there. If so, submit them. Then on the top right you’ll see a little box, make sure to check off Developer Options and on the reports you submitted, you should see a report ID #. If you can include that in a reply or in a support ticket then it will help Brave staff to see what’s going on.