I've got an issue with CPU overload in Pianoteq 6 Pro.

While using Cubase 10 with these specs in the plugin:

Core i7 860 2.80GHz, M14/S5/F6, x4
Host sample rate 44100 Hz
Buffer size 256 samples
Max polyphony 48
Sound interface: Steinberg UR44

it's impossible to load more than 3 Pianoteq tracks in the project. Each project takes around 15-20% CPU and when I load the fourth track it goes up to 100% instantly.
So it's impossible to operate it.

I could think that there are some problems with Cubase, but any other plugins don't have this issue no matter how many tracks I use. And sometimes CPU overload window appears even when I play from standalone interface.

Could you help me with this issue, please?