Z2m 'adding via' one specific router does not work at all

Maybe someone can help me here:

just got a bit familiar with HA and set up my first ever smarthome.
When most things worked as expected and the ZB network was stable I relocated my coordinator to have it behind a UPS and make it a permanent installation in a what I suspected an ideal place.

After restarting the RPi and HA some battery driven sensors where shown without "links" in the map.

They where all linked correctly and routers formed a mesh also before I moved the coordinator.

To optimize the links I wanted to add some devices to specific routers and specific routers to others.
I expected this would be what "adding via" is.
Unfortunately this doesn't work at all.
When I select a router located near or at least in VLOS the device I reset does not change it's parent.

Many thanks for your help in advance!

Trying to force zigbee to route a certain way is wasting your time.
It will route the way it wants to route.

copy. So the feature "adding via" is useless and faulty anyway? May I ask if you know why it's there anyway? Maybe someone should tell this the developer if there is any? Best regards

Did you Reset the Device and pair it with Zigbee again?

I think did. As far as I understood I just had to press the button for (depending on the device) 3-5 seconds until its indicator (or for the Sonoff plugs the network indicator LED) flashes.
Allowed adding via before pressing the button.
Tried "adding via all" as well as via a specific router or the coordinator.
Seems the the whole mechanism is not working at all.
Also tried to remove/readd the batteries.
Also deleted the device in Z2M.
Also checked the DB that the enry is removed.

I am uncertain if there is more faulty stuff in my HA than the ZB part. As I wrote in another thread my energy dashboard started to fail calculating some values prior to the coordinator relocation.