Put the summary of the bug you're having here
What I expected to happen was...:
Only one process instance of the MinecraftLauncher.exe would show up and my game would run smoothly.
What actually happened was...:
When I click on the launcher it opens the launcher screen, before I click "Play" I look at the Task Manager and it shows three duplicate processes each called MinecraftLauncher.exe and when I play Minecraft it goes very slow. Playing last night it was working fine.
Steps to Reproduce:
1. Close Minecraft
2. Click once on the launcher (in the quick-launch bar)
3. When the launcher opens hit Ctrl + Shift + Esc (or Ctrl + Alt + Del) on my keyboard
4. Go to the Processes tab and notice that there are three identical versions of the launcher running.
5. In the Minecraft Launcher screen click "Play"
6. Click "Single Player"
7. Select the world I want to play on.
8. Game play is very slow
So, that has absolutely nothing to do with the game, and is how the launcher works. It is based on Chrome, and uses three sub-processes. This works as (currently) intended.
Your issue with the game being slow is a separate one.