WHen I heard the first prognosis tangled mess is what came to my mind.
I had a simular problem feeding electrical
lines down the wall of a multistory building. I had someone at each floor to insure it was feeding smoothly, but one of the guys was off task, and about 30' of line backed up in the wall. I tried to go back up but it stuck, and tried to break it loos to gon further down, still stuck. When I finally broke down and cut the wall open, I found a ball with several loops intertwined. Once that happens it will go nowhere. Each time we tried to pull it it pulled the loops tighter, and got worse, and damaged the insulation
so the entire spool was unusable, and had to be rerun.
Good you got a look at what you are looking at. if lucky you can find the end and pull slowely until loops untangle, but more likely you will have to cut the entire halyard
out a few inches at a time.