The really light lines can be a nuisance when 3D flying.
I have a set of 30# x 50' and the line is so fine that it tangles around every weed and snagger on the field.
Even worse, it's so thin that it's very difficult to undo the tangles, let alone see which way the snarl goes.
I love 50# in the longer lengths in light breezes, but prefer 90# if I'm doing 3D.
What brand are you using?
I've found Shanti 50# line to be easy to tangle--like flying with thread.
Laser Pro 50# is much better.
I'm more agnostic with 90# line, but for 50#, IMHO Laser Pro is the way to go.
UK folks: come out to Kite Party and stock up on Laser Pro while you're here! It's sold right on the pier.