Strangely enough I had a delivery from MSL lippe in Germany by GLS last week. Tracking originally said out for delivery for Thursday, then later that night got email from them saying sorry we were unable to deliver your parcel, but no reason given, the next day exactly the same thing happened, and it was eventually delivered on Saturday afternoon.
Have found GLS can be hit and miss, depending on who the delivery driver is, some knock at the door and hand over the parcel, some just leave it.