How to check for theme and app conflicts when the Shopify mobile 'Add to Cart' button is not working

This morning, the DTC store customer service reported that mobile customers were getting no response when clicking 'Add to Cart,' while the desktop version was working fine. Ads were still running; if I had only looked at the Shopify backend orders, I would have assumed the traffic quality was poor, but in reality, the mobile checkout funnel was broken. I first reproduced the issue using iPhone…