Okay. Thanks for clarifying the steps that you’re following.
We’re literally on the “same page”, using system-native functions. We’re both following the same procedure to create a PDF from an email.
Given that your issue consistently affects some email messages - and not others - the cause will be the email content itself. Mail can be formatted in many ways; some contain text with inline images - while others may use HTML (or similar) like a rendered webpage. It is this latter category that is likely to be the source of your problem.
As I cannot replicate your problem, I clearly haven’t found a received email message that triggers the issue that you describe. Clearly it would be inappropriate for you to attempt to share any of your received email messages here. As such, you will have the task of identifying the common factor for the email messages that are causing you difficulties.
You mention that you also see the problem with email messages that you are sending. Are these received messages that you are forwarding - or new email messages that you have drafted from scratch? If affected messages that you draft replicate the problem, what in your draft email causes the issue to materialise?