FPS drop to 10 even though CPU and GPU usage at 50%

Any idea why would POE only use 50% of GPU and CPU power, but still dropping FPS to 0 by farming realy juiced map?

CPU usage is 100% only at loading new location. https://ibb.co/K7zLZL


CPU AMD Ryzen 5 2600 Six-Core Processor 3.40 GHz
RAM 32,0 GB
GPU RX Vega 56
Windows 10 Pro

DX12 or Vulkan no change.
Triple Buffering - enabled
Multithreading - enabled