After update my jails were not running. Error when trying to start manually mentioned something about the mounts not being correct. I went in to the mount points and tried to reset them by picking the proper locations in the interface and that didn't work either.
Reverted to U3 and they are working again.
If you have jails set up you might want to wait on U4.
Reverted to U3 and they are working again.
If you have jails set up you might want to wait on U4.