Can't get trainer mode "Axis" to work (SBUS wireless trainer)

[zsdr-bln]

Hi guys,
I recently bought the Radiomaster SBUS wireless trainer. My radio is the RM TX16S and I use a HappyModel EP1 as the RX for the wireless trainer. RX is configured to SBUS and correctly plugged in SBUS_A. When I am setting a special function switch to activate the trainer mode, I can't get the mode "Axis" to work. What strangely works is the mode "chans".

When I am using the wireless trainer in my RM Boxer (RX in port SBUS_B) then the mode "Axis" does work. This leads me to the assumption that I might have a hardware issue with my TX16S here. If so, any chance to solve it myself?

(Using the wireless trainer in my JumperT15 in SBUS_A brings also the mode "Axis" to life, so the trainer module is fully functional)

I appreciate any helping feedback :)