I have a similar issue I am using the debut theme,
Hello! I have the same problem. Sometimes I get a message "There was an error while updating your cart. Please try again." when I try to add products to the cart.
And also this message is written to me if I want to remove products from the cart.
hi I tried to uninstall the messenger app but same problem
Finally someone from Shopify support solved the problem, it was an Shopify app for Facebook messenger that I had installed, I just deleted it and problem solved. Congratulations Shopify team for the amazing costumer service!