In various past posts, I mentioned that I could not configure Roco engines with a Zimo decoder through DCC-EX and JMRI - even though it just worked fine for a Piko loco ... Overall, the DCC-EX command station wasn't very stable.
I thought that the wiring on the test bench could be the issue. Because of the rotary switches, it could be that the track 1 and 2 were actually connected to each other, or something like that.
I made one change by disconnecting the rotary switch for track 2; therefore track 2 is now directly connected to the programming track of the DCC-EX command station.
The green and blue wires come from the DCC-EX command station, whereas the red and black wires come from the rotary switch for track 2.
And it's now working as a charm! I need to find a better solution since now I cannot connect track 2 to the ESU LokProgrammer or the AUX.