I wouldn't worry too much about it.  You're playing in games where most players have no concept of folding.  That means an artificially high number of hands will go to showdown, and you will have to show the best hand to win.  So having a declining red line is more a property of the game you play, rather than something you need to correct.

If it was only about the red line it would be quite easy to increase it.  You can prove it to yourself if you need to.  Just go hyper aggro in some session, and it probably will point upwards.  But you will most likely sacrifice actual winnings while doing so, and I would assume you're not looking to do that.

It's pretty unusual for a winning PLO player to have a positive red-line from my experience, and in low-stakes games where the rake is high and people can't fold it'll be near impossible. Always a good idea to look for areas to improve, but these graphs in themselves don't show a leak that would concern me.

thanks guys, really appreciate it. I might test hyper aggro style before I move to PLO25