Depending on the attachment, it sometimes takes considerable time for the phone to render the document. I have found PDFs to be the worst. If they contain text, good, if there are lots of pictures, bad. There have been cases when I have just given up and waited to reach a computer to check it out. Most of the time when this happens, nothing appears on the screen and when the document starts to appear, I usually see content (some of it at least) quite soon, usually with the difficult cases it takes long time to see a screenfull and when you try to scroll, it takes ages to see the next screen.

"Tabula rasa" appears seldom. Most of the time viewing attachments works fine.

Both .docx and .odt work. Nice.

But to actually help you, I have no Idea. Naturally, if you have developer mode active, you could try to look into the logs while trying to view the attachment.