iOS 13 Mail App - Emails Found in Sent Mailbox - Message has not been Downloaded from Server

We have a Mail app issue with multiple iPhones on iOS 13.1.2. This has been noted on the iPhone 7 and iPhone XS. This is only happening in the Mail App. The Outlook App and other clients work as expected. This issue is not present on iOS 12.4.2. We are connecting to Exchange 2013.

Messages in an email thread that are 'Found in Sent Mailbox', do not load. They state "This message has not been downloaded from the server."

This has become an issue because our users are replying to an earlier reply they sent that is 'Found in Sent Mailbox'. This reply does not contain the email thread because the message was not downloaded from the server -----> the issue.

Nothing has changed in our Exchange environment (I am the admin). Apple support was useless and continually pushed this off as an Exchange issue.

Please help.