That is handled by the ecart definition file. I don't think it is the issue. We use odd characters to separate items to ensure we aren't using a character that might occur naturally. If you can checkout with those characters, then you are barking up the wrong tree.
Reproduce the issue first, then analyze the cart contents when it fails. Analyzing the cart contents when the checkout succeeds won't help you find the cause of the problem.
I'm fairly confident that there are steps to reproducing the issue. Either cart items, shipping settings, or maybe even guest checkout or shipping address. The first step to debugging any issue is reproducing it.