Random Checkout Error Message

[karen73]

We are getting increased sporadic customer feedback this week that they are unable to checkout and the attached error message appears. We have checked out successfully ourselves but on one occasion I received the same error message. Shopify support believed it was a customer browser issue and suggested they clear the cache or try on a different browser, however this did not work. I have noticed a large increase in open Draft orders and am concerend something else is causing the error message. We do have a collaborator working on a draft theme however there have been not changes to the current live theme. We are using a third party app called Hulk for creating chargeable options which does interface with the shopify checkout pages. Before I contact them does anybody else have any suggestion on what might be causing the issue?