I am going to add something hypothetical to this thread which may be related to a 'boot lock' thread I am already posting on.
I am going to assume a problem with the boot lid locking NOT the luggage cover which is usually just the switch for it not making contact.
I am also assuming in Belgium it is cold (freezing) like it is here in U.K. If the boot lock doesn't lock when the boot lid is lowered, the system seems to try locking it. This could be a normal VW security feature.
When the boot unlocks, the lid and (I'm guessing) a switch inside the lock, tells the system the boot is open and it will not try re-locking. If the boot (trunk) lid does not lift up after lock actuation, the system will think the boot lock has not locked and will try again. The boot lid should have some upward tension from the two gas spring struts which allows it to lift up slightly when the lock is unlocked. In very cold weather the amount of lift from the two gas struts, especially if old, may be insufficient and the problem gets worse if the boot lid is iced over (heavier).
There are a couple of things to try. First push downwards on the boot lid then try to lock it with the fob. If the motor whirrs once and the boot locks that is o.k. Then apply some upward pull pressure to the locked boot and operate the remote. If the boot unlocks with one 'whirr' and no warnings then that is o.k. In the last test you are compensating for reduced gas spring tension. In the first test you may be finding that the two adjustable rubber bump stops that set how far the trunk goes into the lock are set slightly too high. But you have to be careful adjusting those, because I think they also determine how much the lid is pulled down by the lock motor and contact pressure on the boot seal, which must be even all around (no gaps).
As I said, this explanation is hypothetical so try out the ideas. I am waiting for a new pair of trunk gas spring struts to arrive to be able to do some tests. These are dirt cheap and 5 minutes to fit if they solve your problems.