Plugin cart66 Pro: "Your Cart Is Empty" inconsistently occurs

Hi, I am having an inconsistent issue with my cart working and then not working. And, it appears that at the same time it is working for me, it is not working for someone else, and vice versa. I did find a post from about 8 months ago that addressed this, but none of those solutions worked for me and this is a much newer version of everything at this point.

The site is a subdomain with it’s own cart at https://tickets.lauracrisci.com and it’s rather basic (I also have a separate cart on lauracrisci.com that works just fine). When it works, it works flawlessly. When it doesn’t work, nothing happens but “your cart is empty” regardless of the selection you make.

I’ve tried deactivating and reactivating the cart. That seemed to work the first time I did it, but the next day it stopped working again and that did not resolve it.

Last night, I also tried deactivating and reactivating the Thesis Theme as well. I also disabled caching on cart pages in the ‘Error Log And Debugging’ in the cart66 settings, and soon after it started working again.

This morning, it is not working again. I’m stumped. I don’t understand how it can work and then not work and work for me and not someone else and then the opposite. I’ve got to fix this somehow by this week. Any help would be greatly appreciated, Laura.

Here’s what I’m using…
Thesis Theme 1.8.2
Cart66 Pro Version: 1.3.3
WP Version: 3.3.1
WPMU: False
PHP Version: 5.2.17
Session Save Path: /tmp
MySQL Version: 5.1.56
MySQL Mode: Normal
Table Prefix: wp_
Tables: All Tables Present
Current Dir: /home/lauracri/public_html/tickets/wp-admin
WP Url: https://tickets.lauracrisci.com
Server Name: tickets.lauracrisci.com
Cookie Domain: tickets.lauracrisci.com
Curl Test: Run Test
Write Permissions: Writable