It is probably an extension of some sort.

I have heard this can happen with Privacy Badger, but I'm sure other extensions can cause the issue. I think it is a fairly common issue with embedded Vimeo videos, but I haven't had a chance to look at alternative options/settings and hosting videos myself comes with a whole other set of issues.

Just FYI I am not personally doing a bunch of tracking here. I don't even think I have Google Analytics setup on this domain. Instead it is a byproduct of Vimeo having at tracking cookie :(