No Spend/Impressions/Taps/etc. in one identical campaign

I have nearly identical campaigns that only differ in the location and a few keywords, but my UK campaign (which I only recently unpaused) has had zero spend or impressions (running since Monday).

This is very strange to me since my US and Germany campaigns always perform comparably. I would expect my UK campaign to be slightly different, but zero impressions is impossible.

Is it possible that this is a bug?