One thing we have to give Facebook, they are consistent. Facebook has just announced that they have discovered two new measurement errors that resulted in advertisers paying too much. This makes the total number of these kinds of error 12, since Sept 2016.
The two new errors are related to mobile videos (including video ads) playing out of view. This has meant that a number of advertisers have been overcharged for ads that no one saw. If you are wondering what the magnitude of the error is, a spokesperson has confirmed that a couple of hundred advertisers will be receiving credits that exceed $5,000.
Error number 1 only affected videos that were loading on the mobile site for Facebook. Essentially, videos are supposed to stop playing once you scroll out of view or the viewer switches tabs away from Facebook. However, some videos continued to play in the background giving false viewing stats. Only a small percentage of Facebook users access the site through the mobile version, most mobile users use the official apps.
Error number 2 was a little larger in scope and affected videos that were embedded in Instant Articles. If you were on a slow internet connection, you could scroll past an Instant Article without viewing the video. In these cases, the Facebook app is supposed to preload the video in the background, but not actually play it. Well, you guessed it, they played anyway causing false viewership numbers.
Facebook is refunding any affected advertisers and is releasing a fix to correct the error.