I had noticed some weird “no impressions” effect a couple of weeks ago, but at the time I couldn’t pin it down to a specific word yet.
However, now I am pretty sure that using the word “download” in your Google ad can trigger their “manual approval” process. Here’s what happened:
This Saturday I added new ads to a series of ad groups, for testing new ad copy. When I checked the ads a couple of hours later, I noticed that some of the new ones hadn’t received any impressions yet (these are high volume ad groups, so that was weird).