Floating Fly Line

Are you sure the line is a floater?

Op's suggestion about water seeping in through cracks in the line is
possible. If it's a poor quality line with cracks over its useful
length then it will sink.

It is also possible that after a few hours use - in a lake - the line
is covered in slime, scum and goo that causes it to sink. In which
case a good clean and treatment should get it up on top again.


Steve

You can let the flyline set for several days--stretched out--and again seal the bond to baton affiliation with adhesive or adhesive to see if that solves the problem. While in the stream, if your flyline begins to sink, apocryphal cast that band several times to force baptize out the en of the line.