See my movie
Delivery of wagons to a stubline is controlled by a profile in my system and works very well.
but how to manage to drive the locomotive back to pick up wagons when the block is busy
Anyone done that? Any tips?

HI, that is often the problem with the single detector policy and axle detection.
I have not equipped my carriages with axle detection, so the sidings are occupied because the name of the train is present, but the current detection detector is inactive.
So when the detector becomes active because the locomotive wants to pick up the carriages, WDP knows the position of the locomotive and can stop it at the buffers of the train to be picked up.

https://youtu.be/ZQTnaXR6dvY

It is better to install a second very short detector, which can be a current detector.  Or a so-called reflex light sensor, such as the Zimo SN1D.

However, a Hall sensor or reed contact can also do the job.