First of all, the rating system changed since 2014, therefor your problem has nothing to do with the initial problem of this topic. Please open a new topic next time if the last post in a topic is ancient.
And in the new rating system, your rank can drop by some points after a game, since the rating system calculates your rank by looking at your up to 15 last games. If the rating of one your opponents changed in between, your rating can drop, even if you won the last game.
The math of the ranking system is somewhat arcane. Therefor I don’t explain it in detail here. If you really like math, send me a message and I provide you detailed information.