Logic + MIDI + LP = I need Help

Hello,

I have a LP, I had one single MIDI cable at the time, so I set the LP up as a MIDI controller, and routed the audio out of the LP into Input 1 on DUet.
I am able to record MIDI, hear the synth, but not playback the MIDI with the synth because at the time I had only 1 MIDI cable.
Now I have 2 MIDI Cables, 1 MIDI out of the LP, and 1 MIDI IN coming back into the LP.
Now if the playhead is not moving I can trigger the synth and see MIDI activity as normal.
The second I hit play on the song I am not able to trigger any midi activity and I can not hear my synth.
THis does not occur if I unplug the MIDI cable that is going to the “MIDI IN” on the LP
Please, any suggestions or help. I have been trying for hours, and just need to be able to record midi and have it playback.