It sounds like your sleeve/knot may have slipped on that line. If the line is sleeved you can un-tie the knot and then re-tie the sleeved line in the
proper place once again. Most sleeved lines are tied off with a single overhand knot and although this usually is more than sufficient to hold, I
prefer to tie a second overhand knot right next to the first just to make sure that the sleeve does not slip on the line. Remember that each knot you
put in your sleeve will shorten your line about 1/4" so if you add a knot on one line you will want to add the same knot on the others so they will be
equal length.
If your line is not sleeved then I would suggest sleeving it. Spectra line is naturally slippery and can even have a wax-like coating added to
increase the slipperieness of the line. Usually a knot on specra line will slip or break as knots on spectra can reduce the strength of the line by
as much as 50%. Sleeving the spectra line with a dyneema sleeve will help reduce the amount of strength loss with the knot and will also help keep
the line from slipping through the knot.
Hope this helps.