It might have just been similar to an "eye" lead.
The other possibility is that you had "hooked" the shackle or lead on part of the furling drum -- then you dislodged it with a "bang".
First, if it's not marked currently, I'm make a mark or place some reference tape on the halyard. This will allow you to reproduce the current halyard tension. You can put a piece of tape on the mast and then a piece on the halyard. Use this to figure-out what's going on with the hoist.
I think then I'd unfurl the jib and lower it to the deck. Then look at how that uppers portion of the rig looks with that gear on the deck. Check, if the jib has an extension piece (do deal with a partial hoist), or you might see some sign on the head wear of the sail, and then look at the halyard and shackles.
This would allow you to see if there was something going on from below with your binoculars.
Then I'd re-hoist the jib and try to furl it with the furler.
Then, you might go up the rig. (I'd use the main halyard to go up the rig.) Then, while you're up there, have the sail rolled out a little bit and eyeball what's happening.