Indeed when loading Matrix 12 V the first time, sometimes voice are 'skipped' i.e. not heared. This happened to me in demo mode (I was thinking this would be part of the demo limitation). But later it also happened after authorisation. Depending on the patch loaded, different voice numbers would be skipped, most cases just one or two out of all voices. In a particular patch always the same voices would be skipped when rotating through the voices, so it is not a problem of one or more specific voice numbers only all of the time for all patches, it varies per patch. I've seen voice 1 being skipped in a particular patch, but also voice 3, 8 and 9 in another patch, and so on.
After reloading the plugin into a channel strip the problem seems to be fixed.
For another test I started up Logic again and played the Matrix 12 V on initial load. Same voice skipping again. After removing the plugin from that channel, and reloading the plugin again on the channel, voice skipping disappeared. So reloading the plugin a second time after initial firing up seems to temporarily fix the problem.
(I'm running MacBook Pro 2.4 GHz Intel Core i7 with 8GB RAM and OS X 10.9.5)