[Hummingbird] Hummingbird breaks WPMU MarketPress Store

After applying all Hummingbird performance actions, WPMU MarketPress Store shows a spinning circle each time the website is displayed. Clicking anywhere on the page outside the spinning circle makes it go away. I've disabled the MarketPress Store plugin for now, but it's okay for you to reactivate as needed for testing. Note - there is high customer impact when the MarketPress Store plugin is enabled, so testing should not be conducted during USA Central time 7am-10pm.
Please let me know if there are any additional items you need for research.
Screenshot: https://www.dropbox.com/s/2984trtlkcmgeav/Screenshot%202018-04-22%2012.46.35.png?dl=0
Many thanks.
Bob