Well, I think I figured out what's going on but don't know how to fix it. I attempted to forward one of the emails without the attachment in the Gmail account on my Surface to my live account. As soon as I hit the forward button I received a prompt that said the message hasn't finished downloading and had a button to finish downloading or continue. If I hit finish downloading I can see the attachment.
This is good but now why does this only happen with some attachments and what do I do so it always downloads?