I don' t know what kind of broadheads you shoot but I had an similar problem back years ago.I thought you could put on matching field tips and practice.Then when season came you put on the broadheads and hunt[X(] wrong on my part.
I went to pull my bow back on what possibly could have been my first bow kill when my arrow poped off just before full draw similar to your problem. My problem was my broadheads were catching on my riser and pulling off the string. I also put the arrow on and tried it three more times before finding the problem.
The problem was my arrow rest had gotten bumped in towards the riser and as I drew my bow back my broadhead (Muzzy)would catch the riser and pull it off the string.You might check to see if that could be your problem.