Looks like something trying to open an ad that it can't connect to.
What apps did you install or update in the few days before it started? Because if this is popping up at random times, rather than when you try to open a particular app, you may have an adware app on your phone (which could be a new one or it could be a previously OK one has changed with an update). Though it's worth clearing all of your browser caches just in case it's simply an advertising script that was downloaded from some site you visited.