This has been our experience as well. In my brain, many issues started when Chrome/Google updated their security perimeters. I could not log onto various government sites plus stopped receiving invoices (randomly) from vendors. Our IT department white-listed Intuit plus I cleaned my cache and cookies, both have seemed to help with the overall issue. So, my point, your customers are the ones who may have to do the work in order to receive the invoices. I was tired of vendors making accusations so I figured it out on my end. 

The bottom line is Quickbooks does need to resolve the security issue.