How can it be fixed when a user sometimes does not receive attachments in contract approval emails?

Summary:

We have a production issue: a Financial Planning user (the only one receiving these notifications) does not consistently receive email attachments in Oracle Fusion contract approval notifications.
In some cases attachments are delivered, but in others they are not. We have confirmed with the infrastructure team that there are no email blocks, and resending notifications does not resolve the issue.
We also verified that there are contracts with multiple attachments totaling up to 16 MB that are not being delivered, as well as others with files around 7 MB that also fail to arrive. So far, the only workaround that has worked is compressing the files before sending them.