I had same problem and was able to correct today by clicking on "Help" in the top menu of the pop up box that displays the "This XML file does not appear to have any style information ...."
Then click on "Reset App Data"  > after a 5 second countdown timer goes away and qbo app shuts down > restart the qbo app > it will ask your for login credentials > then I was able to access the attachments.

Not sure if it works for others ... but it did for me!