Simple issue, when rendering in place from external instrument it fails if there is a drum map assigned. Took me years to work it out.
To reproduce simply create instrument track using an external instrument, assign a drum map, try to render in place, nothing. Remove drum map, bingo it renders fine.
Is the MIDI channel in the drum map the same as the MIDI channel being used. Loading a GM drum map I think has all of the sounds on MIDI channel 10 and your drums may not be on that channel.
It doesn’t matter what channel the tracks set to, if there is a drum map assigned, and your using an external instrument, when you click render, nothing happens. If you disable the drum map it renders as it should.
When I say nothing happens, Cubase just ignores the render request completely, it doesn’t even try to play the midi part.
I spent hours and hours trying to solve this and FINALLY ran into your comment which solved the render-in-place issue. How very strange this slipped through beta testing. Thank you so much!
No thank you, I was beginning to doubt my sanity as no one else seemed to be having this problem. 
Oh, don’t worry. I can reproduce it, too.