Did you use powdered cinnamon? Cinnamon can cause a mucilaginous substance to form in cider/wine/mead. It doesn't always, but it's most noticable when powdered cinnamon is used. The only other thing that comes to mind would be a bacterial infection. Have you noticed a consistency similar to eggwhites in the must? Sort of an "oilyness or ropiness"? That is a telltale sign of bacterial infection. Here's what Jack Keller had to say about bacterial infection:
"Oiliness or Ropiness: The wine develops an oily look with rope- like treads or strings appearing within it. It pours slowly and thickly with a consistency similar to egg whites, but neither its smell nor taste are effected. The culprit is a lactic acid bacterium and is only fatal to the wine if left untreated. Pour the wine into an open container with greater volume than required. Use an egg whip to beat the wine into a frothiness. Add two crushed Campden tablets per gallon of wine and stir these in with the egg whip. Cover with a sterile cloth and stir the wine every hour or so for about four hours. Return it to a sterile secondary and fit the airlock. After two days, run the wine through a wine filter and return it to another sterile secondary. Again, this problem, like most, can be prevented by pre- treating the must with Campden and sterilizing your equipment scrupulously."
I'm not saying it IS an infection, just saying it MIGHT be. It might also just be the cinnamon thing. Sorry I couldn't help more. Regards, GF.