shipment planning with late pickup date instead of early pickup date

I have a question and hope that somebody else experienced the same.

We have some orders that are planning with Late Pickup date being a start time on the shipments. This is causing quite a bit of issues with not being able to schedule appointment for that day and have to change the date. It does not happen for all shipments. Some shipments are planning with correct start time. We use the same planning parameter for both cases but results are different. I checked HOLD AS LATE AS POSSIBLE parameter and it's false on the parameter set.... is there anything else i need to check?