You can manually fix this in BAM by going to boincstats, and following the links: BAM! -> Project List -> WCG's show hosts button -> Removing delayed detach, no new work, and re-adding attach.

BE WARY HOWEVER. This causes your client to reattach to the insecure http url, which likely was trying to be moved away from. So if you change it manually now, you might need to change it again manually in the future to switch to https once the bug in BAM is fixed.