One question - do you have to rethread because the thread is breaking? Silly as it sounds, this happened to me once and I eventually cured it by turned the spool of thread upside down so it rotated in the opposite direction. I can't figure out why this would make a difference, though. Maybe I did something else different at the same time that really fixed up, but this is the only thing I remembered doing?
PS: I had not been drinking wine at the time.