My trick for fixing software is "If you can't fix it, break it more and use effects of your damage to learn about the system and see what you can affect."
That’s often my approach to diving into performance problems too. When a client says “it starts to slow down a bit at 2 requests/sec”, my first thought it “what happens at 20req/sec?”
I call it “turn it up to 11 and see what breaks”