RE: Marketing Page Mobile Optimization Not Working
Hi Joey,
Did you create marketing email from scratch or from existing templates?
In addition to meta tags you added, please also check whether media query attribute has been nested within style tag,

and check whether your image elements has been applied with corresponding class name to be responsive on mobile device.

The appearance of email on different clients will be different due to compatibility,
for example, email layout is responsive in Gmail App, while not on Gmail Web,(iOS) due to media query attribute is ignored on Gmail Web.
Try testing whether the issue will also happen if the email is viewed in email application when both media query and class name were added.
Regards,
Clofly