The PAB isn't compatible with the Microsoft O365 User Submissions portal when the reported email has an attachment. When the reported emails has an attachment, the PAB will deliver the email to the reporting mailbox and attaches both the packaged up .EML/.MSG email file and separately attaches the attachments themselves (e.g. .exe, .xlsx, etc.). Microsoft documentation clearly indicates that emails with more than 1 attachment will not be scanned, so there should be a setting in the PAB to only attach the .EML or .MSG file (which already has other attachments inside).
Removing the redundant non-eml/msg attachments would all us to both use the PAB and have Microsoft scan the spam/phishing reporting mailbox for threats to continually improve security.