We coincidentally were experiencing a similar problem last week on version 9 while trying to bring some project files to another facility. While I haven't had a chance to test yet, I think it was being caused by 1080 files being scaled down in the project output to 720, not sure what kind of resolution you had your animation at.
I would submit a ticket though since there could be some logs that tell a better story in your case.
#XPression