Hi Howard,
When that happens to me, I make sure the B4a bridge phone app says "Waiting For connections". I also check the ip address the app found. In B4a I check to make sure the ip address from the phone app is in the list of previously used ip addresses. If I find one, I select it and I get a connection. If I can't find any, I add a new one and that usually works.
Hopefully you can connect.