The fact that the tempo pops up the first time suggests that it is receiving the first CC.

It may be some running status issue – don't know whether the GCpro does this (manual doesn't say). To test this, set up the other switch for some other CC (doesn't matter which) and press them alternately to see if the TT then works. The alternating CCs will defeat any running status sent by the GC. Let me know ..

Running Status – this is a MIDI feature where the first part (called status) of a CC message is only sent once – thereafter the second part (the data value) is the only thing that is sent. Sending any other CC resets this mechanism and send the first part again. TF supports running status, but you can imagine that there is a potential for problems.