100% a known issue. They haven’t really addressed it via patches either. Knowing that, you should also know that it is better/worse in some aircraft over others. I can’t go above 4x in the King Air. But I can hit 8x or 16x in others. The issue has changed patch to patch for some aircraft over others.
This makes me change behavior in the sim. Instead of throttling back when running longer hauls, I will disable engine damage and fly at max speed. 4x at max speed is still better than 4x with fuel saving cruise speed set.