So I've seen this graph:

https://forumserver.twoplustwo.com/cache.php?img=https%3A%2F%2Fi.gyazo.com%2F2de0e845d02817160ade20b304a3d3e9.png

I know, all that matters are the winnings or the bb/100. However, I really notice that my redline is often times simply terrible. I feel like the winrate almost lies in a decent redline. I guess it doesn't need to be positive all the time, but it shouldn't be negative either, right?

What are the biggest reasons for very bad redline?