IOS Mail sub folder issue

My IOS Mail Sub folders are all set up in my Yahoo account. I use this setup because Yahoo gives me virtually unlimited storage.

When I move mail with attachments from my inbox to one of the sub folders I see this in IOS mail:

“This message cannot be displayed because of the way it is formatted. Ask the sender to send it again using a different format or email program. multipart/mixed”.

If I look at the item in the Yahoo Mail app sub folder it is correct, including attachments.

Same issue in my iPad Air 6 and my iPhone 14. Any ideas why this occurs?