You have configured an insertion policy in Pulse that says the ad server should always return only one pre-roll upon an ad request. However, when making a request, Pulse returns two ads in the ticket response, and two ads are shown in the player.
The most common explanation for this is that you have a sponsor goal in your account that has been incorrectly targeted, allowing it to run anywhere. Sponsor goals are used for extra sponsor messages and guarantee a prime position directly after ad breaks in pre-rolls and mid-rolls, and before post-roll ad breaks, meaning they are delivered closest to content.
Sponsor goals are always shown in addition to the insertion policy. This means that if you set an insertion policy to one pre-roll, Pulse picks one normal goal for that position, but it also has a sponsor goal booked. This goal is delivered after that one pre-roll on what is called the "sponsor position", which is always outside of the normal pre-roll break and therefore not affected by insertion policies.