Intermittent Blank Page After Order Submitted for Payment

We have some customers calling and complaining about a blank page after submitting their order. Sometimes the customers hit the back button and resubmit, resulting in duplicate orders that we have to refund. Does anyone have any idea why this may be happening to only some people?

We are running WC 3.1.0 as the newer versions breaks our site. We also use SiteGround’s Super Cache, which by default is designed to work seamlessly with WC though we have /checkout/ assigned to not be cached. Our site has 100% uptime when these issues occur.

Really would like to solve this problem as it only happens to a small percentage of our orders though creates a lot of extra work communicating with customers, cancelling orders, applying refunds, etc.