I'm having kind of similar issues.
I run Native in Studio One Pro 3.51 with an i7-7700 Quadcore 2,8 GHz and 32 GB. Interface is a Presonus Studio 68 at 48 kHz.
Opening a blank session, only one mono-audio-track. CPU at 3-4%. As soon as I open a Native Instance the CPU jumps to 50% Minimum and is frantically jumping around up to 100% in peaks.
As soon as I turn of Native the issue is gone. Increasing buffer size helps but does not really solve the problem (still around 30% CPU).
Any Ideas anyone or do I simply have to wait for future fixes?
By the way, Helix sounds exactly like my LT and Helix Floor. Did a High Gain-Side-by-Side-Comparison. No audible difference. Looking forward to a fixed Release