Hard to say, over 80%  users here use Helix Ultimate for their projects. And most of them get very high score in Google Speed test (85%-98%). I also use HU for my private sites, and all works smooth.
So it can be something  else that slow you down.  It request error logs investigation and debugger mode in your case. You can always use our older, Helix3 for testing period. 
You can also ask hosting support what it can be, maybe sort of security settings, who knows.
If it would be a common issue all users would have it, right,   but no similar topics so far.