My frame rate dropped while adding objectives to the scoreboard system.
I started with a frame rate of 160 per second after the 10th objective it slowly started to drop. I was not moving at the time, also there were no new chunks loaded, entities spawned or moved nor any redstone contraptions running.
After adding the ca. 15th objective the framerate was already only at 30. It dropped further while adding more objectives, at 20 objectives in a row it was only at two fps.
A relog helped both though, it got my frame rate up again and kept the objectives, still i wanted to report it, just in case.