Hi, Scott. Thanks for the detailed question. Sorry you’re experiencing this.
I’m not sure how the CSV import process might be different if you have PRO active, but I do see that you’re on PHP 5.3, which does not meet WordPress’ requirements.
We require the same system requirements as WordPress does.
Please upgrade your version of PHP and try again.
If it doesn’t work, please disable all non-Modern Tribe plugins and test again while PRO is active.
Another idea is to enable WP_DEBUG and WP_DEBUG_LOG and share any debug messages you see while changing tickets quantity, navigating your site’s home page, events page, single-event pages, and any other of your site’s pages relevant to this ticket.
You might also see if you can spot any console errors at your site. (If needed, you may reference our KB article Using Google Chrome Developer Tools.)
Please let me know how this goes for you.