I have now found the simple answer to my initial problem:
When I close my project residing on the Bome Box in the Configurator, the most obvious of all routes, namely the MIDI DIN IN as source and the MIDI DIN OUT as destination, is NOT automatically restored. That was the reason the MIDI did not arrive at the Translator Pro ALTHOUGH the LED on the BOX indicated that MIDI was coming in.
Anyway, it would be even more logical to give back the communication authority to the Translator Pro whenever no project is activated within the Bome Box itself. But this is not the case for whatever reason.
This is the most confusing device I’ve ever seen, but very useful.