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.