The first several times you play a new game, you may see a drop in your LPI. While we weigh games less that have been played only a few times, they will still have some effect on LPI initially. This means that when you play a new game a new number will start to be included and affect LPI calculations. Since users often have lower scores the first few times they play a game, it is normal for LPIs to go down after playing a new game. Additionally, when we remove a game from Early Access and assign an LPI to the game, it will begin affecting your LPI calculations.
Each new game you play tests one of a number of different skills and contributes to a broader picture of your Lumosity performance. You shouldn't be discouraged when you see a new game bring down your LPI, as this is perfectly normal. You shouldn't expect to perform as well in a new game as you do on games in which you have more experience. You may want to continue working on that game to bring your LPI up.
It is important to keep in mind that the object of your training is to improve your cognitive functions; the games are just a fun interface to allow you to do so. Regardless of your scores, you're still giving yourself a great mental workout!
For further information about LPI, check out the FAQ "How is LPI calculated?"