Q: Instrument track is not added in mixer

In you mixer, make sure you either have the Tracks button or the All button pressed:

Your video requires unregsteried users of that site... to install a windows app to download it..

Not that useful for mac users huh?

Can you not just upload to Youtube and post a link to the youtube video here?

That's very strange. Have you examined those notes in the piano roll, or in the Event editor?

As Erik suggested.. open the event editor and look for Vol entries there.... for example that could be interfering with things..

If you have an iPad or iPhone and have used any Logic Pro related apps.. turn them physically off, leave them off and try out Logic Pro again...

Next, if that doesnt fix things.. shut down your Mac and unplug any midi controllers you may have.... and then test again

Finally, try the true and much tested 'delete prefs' method...

http://support.apple.com/kb/HT5859

and specifically this part....

Delete the user preferences

You can resolve many issues by restoring Logic Pro X back to its original settings. This will not impact your media files. To reset your Logic Pro X user preference settings to their original state, do the following:

1. In the Finder, choose Go to Folder from the Go menu.
2. Type ~/Library/Preferences in the "Go to the folder" field.
3. Press the Go button.
4. Remove the com.apple.logic10.plist file from the Preferences folder. Note that if you have programmed any custom key commands, this will reset them to the defaults. You may wish to export your custom key command as a preset before performing this step. See the Logic Pro X User Manual for details on how to do this. If you are having trouble with a control surface in Logic Pro X, then you may also wish to delete the com.apple.logic.pro.cs file from the preferences folder.
5. If you have upgraded from an earlier version of Logic Pro, you should also remove~/Library/Preferences/Logic/com.apple.logic.pro.
6. Restart the computer.

Then test again

Ah, yes, only now I notice that the notes do get played by the track above it - that's even weirder, though at least they aren't 'lost', just displaced. Still, it's very strange and I can only diagnose it as "project corruption".

It might help if you could upload that project somewhere for Nigel (TAOS) and me (and perhaps others) to investigate.

The problem is related to some kind of side chain you have set up in that project

Not sure exactly what you have done but it looks like you sidechained Ultrabeat in some way to other tracks...

Create a brand new project and test and i am sure the problem will go away... which proves it is a project specific issue and not a general issue with your setup...

Additional..

It looks like you set up some kind of sidechain involving Audio 1 for that project..

I dont have time at the moment to research into this too deeply but that is what i see when I look at the environment and the full mixer display...

I must say, I've just looked at it and I cannot make head or tails of it, the environment to me looks standard, no extra objects, no different routings, yet all recordings on other SI-tracks end up being played by the Ultrabeat track, even though when playing those tracks live, they do respond directly (as in the video's).

I just made a third SI track, and the notes recorded on that are also played back by the UB track. The Sidechain in UB is inactive. I cannot find the routing of this. I'm baffled.

Did you start this project from an empty project, or from a template?

Also, in the piano roll it says "side chain gate" but I can for the life of me not discover any gate or active sidechain.