Since there isn’t enough complexity in Google’s Adwords ranking system, towards the end of 2013, Google decided to change how it calculates its Adrank (Ie the position you appear on the search results page). Yes your bid is important. Yes your quality score is important. But there is now another factor in the mix and this third component is, quoting Google directly, “the expected impact from your ad-extensions and formats”. And yes… it is truly as vague as how it sounds.
So if all things were equal and there are two competing ads with the same bid and quality score, then the ad which is deemed to have the most positive expected impact from extensions will in most cases, appear higher. This all sounds a bit here-say but Google does kind of make it easy in that they will generally show the highest performing combination of ad extensions and formats as it deems appropriate.
What you can do to fix it:
Use the ad extensions, use them all and try to incorporate them into every one of your campaigns. Don’t do it.. then your competitors are already one step ahead of you (literally!).