Although I don’t upload to vimeo, I believe it might be Vimeo’s fault for causing such a problem. Have you tested to upload it onto youtube as a test to see if it’s the website’s fault? I upload to youtube and personally, I never see any problem with syncing and when you said that it works on your computer and syncs just fine, then I personally believe again, that it’s Vimeo’s fault. But if I were you, upload it to youtube as a test and see if that works well.
Hope this helped.