I can't understand the slack bottom line either,, a couple of inches maybe but when it's yards ? it's very strange indeed, fks up the net so it does ,, fk setting with a wind that line will rise and blow around like an old torn pair of Y Fronts ,, I've re-rigged quite a few nets with the same problem you have ,, as you say it doesn't take long to sort but I'd rather not have that problem to start with .
Regards.