It`s the ventilation [the way the hairs are tied in to the lace]
When the system is off your head, wet the hair and lace--not dripping wet, but wet enough, then direct hot air from a hairdryer onto the knots in the problem-area, whilst pulling the hairs ` down` in the direction you need them to lie in with your free hand---it can be handy to pin/secure the system to a polystyrene head-form [lace side up] to `hold` it while you work on the problem-area...that should sort it out.... also, when it`s fully dry and you`re happy with the hair-direction, you can apply knot -sealer to the knots [ apply very, very sparingly by simply dabbing at the knots with a cotton pad which has some knot sealer applied to it] and this should help ` lock` the knots into that required direction...... just try the hot-air thing once, and see how it ` behaves` [you may need to redo it ]..once it`s sorted, you can then use knot sealer to hold it /prevent the hair from ` moving` again.