Currently in 7.5 star difficulty and character level 66. Maxed out all level upgrades in base, have 100% crit chance bow dealing 195% crits, and firing arrows over twice a second. I could keep going to see if this stops at 10 stars... but meh.
Also, Before one combat I got a notice that there was a cave, and then I got two incredibly difficult combats in a row, followed by the combat I was already going to take. Extremely frustrating, specially because I had already reached the ocean segment of the game.
You can avoid the caves if you notice them. Click the "X" on the top right. We'll make this more obvious with a leave button as well.