Well, openXLib and closeXLib display the same behavior, which doesn't make much sense to me. I thought perhaps I was on the wrong track with it being a printomatic error, but everything keeps pointing back to that. There was a box flashing right before each hang that was there and gone too fast to read, suppressing error messages on printomatic got rid of that box, and now the application actually goes to "Not responding" and will eventually shut down without a force quit.
I've dug and dug through my variables and everything else in the application and am not finding anything accumulating data. I've tried removing various sections of the document to see if a particular layout or content was triggering the problem. All that does is effect how many documents I can print before it crashes. Removing different amounts allows more or less prints before crash. Removing a small amount allows one more print before crash, removing half the pages allows about twice the number of prints... all of which points to some sort of memory leak or data accumulation in printomatic, which makes no sense when using closeXLib after each document, it really shouldn't be retaining previous instances of printomatic objects.
Of course, searching through printomatic.com site, I see other people directly asked them about this problem years ago... and never received a response. Amazing the lack of support on a $350 Xtra.
So it's looking like a design flaw of the Xtra, with no apparent workaround besides restarting the application every X number of prints, so I guess it's time to redevelop our internal applications in a more modern language.
Thanks for your time and attempts to help!