I'm using Omnisphere with Logic Express 9 on a MacBook Pro. For the most part everything is great and the sounds are absolutely awesome, but I have one file that has a persistent problem: It starts playing for a few seconds, then audio drops out completely - no error message from Logic or anything else - then, sometimes, audio will come back in a few seconds, but one or two tracks are silent. The Omnisphere instrument on those tracks won't make any sounds at all. Sometimes, when the audio reappears, the problem tracks are much louder than the rest of the tracks instead of being silent.
Memory and CPU aren't a problem; it's using less than 50% cpu, and there's plenty of memory left.
Any idea what could be causing this and how to fix it?
...FWIW, this problem appears to happen only with user patches that were created with an earlier version of Omnisphere. The behavior is new with the latest version, and it never happens with stock patches.