Soloing issue

If it were not for the fact that closing and opening the project seems to "fix" the problem for one shot, I would say that some other blank non-drum track was also being soloed and you are somehow missing it, and then suggest you experiment with the various flavors of soloing and buses, and take a look at the "Track Manager" to look for hidden soloed tracks or some such thing.
 
BUT if in fact it seems to work one time upon opening the project, I would do one of two things:
1.Save the project under a different name and do some severe experimenting. Delete tracks. Delete all plugins. Add or get rid of buses. Anything you can think of.
 
2. Start over with a new project, and if possible add the 33 tracks one or a couple at a time, making sure to test opening/closing/soloing as you go.
 
I personally might spend a little time on (1.), but then quickly go to (2.) if no results.
 
ALSO: I, to am having increasing instances of X3 pro freezing on startup. It starts to load, but then my CPU shows low or no activity (so it is not grinding away trying to start...It just gives up). I click on the upper bar of the X3 window and it says "Not responding". I close and then end the session in the "Program not responding" windows dialog. This has slowly been getting worse, and is quite bad now since upgrading to EZdrummer2. I am running Windows 7, and will be going to 10 soon. I am hoping that helps.

have you looked on the control bar at the MSR module ? you might be able to tell if some other tracks are accidentlly getting solo.
 
have you created any "groups" ?
 
if you are indeed running in to a bug (which I cant say you are for sure)
a band aid for now might be to instead of using solo, run the whole kit (all pieces) to a bus and use that solo finction instead (solo the bus will solo all drums parts)
 
I would get a close look at other tracks when you turn solo off your drums.
it IS possible there is something getting solo's along with your drum folder, thus muting other tracks.

brundlefly
Any Aux tracks in the project? I ran into a particular case where an Aux track remained invisibly soloed after using Global Unsolo in such a way that it silenced the project. If that's the issue, toggling the solo button on the Aux track on/off should restore signal flow.

Thanks!! that did the trick, it seems :-) I replaced my aux'es with busses, and it seems to have fixed it. Still strange it worked after I restartet the project (and did nothing else in between) before! still maybe a bug?