Hope I got this kinda right, haven't used Renoise much lately.
When you use one (instrument with a) FX Chain in more than one Track,
or when you use one instrument plug-in in more than one Track,
then the sound output of it will automatically be routed to the "Current Track" - a setting which you can also change to point to a certain Track.
Problem in your song:
You are starting to use Space Piano on Track 1 and 4 at the same time, but Renoise will not duplicate a FX-Chain or instrument Plugin or a resource like that just in time. There is only one. And it's not being split into to Tracks (channels) either. It has to go into one Track only, and "Current Track" means Renoise choses the Track you play a note on, so that quickly becomes only Track 4, and it will continue to change again and again.
At the beginning of that song, you will think you would hear Tracks 1+4, but when you drag the mixer faders you'll see that you hear only Track 4. That is why the rendered file for Track 1 is mostly empty.
A) Set the FX Chain (and/or Plug-In) output (that is drop-down field on the right side) to the Track number. E.g. Space Piano + it's FX Chain => Track 1, Electric red + it's FX Chain => Track 2
B ) Use more note columns in a Track. Click the little [+] button to get another column in a track and put notes to there, you'll end up probably with only two Tracks
C) In your song, if you're after the FX-Chain/Plugin being applied to each seperate track for a mixdown in another DAW, Solo (right mouse button on [PLAY]) and render each Track for its own. The "Current Track" setting will then be 1,2,3,4,5 but you need to start the 5 renderings seperately.
Edited by Mark2, 09 October 2017 - 06:17.