Lag in viewports but not in floating viewports?! with video

While performing tasks in all main viewports i have huge stutters and lags,
and i wonder why since i have
4790k cpu and 970gtx gpu 16gb ram.

THEN! by accident i noticed that if i make an extra floating viewport, Its completely smooth while in all main viewports its heavy lagging…

See video ( Maybe the difference is not as clear cause of framerate video compression but it should demonstrate the problem clearly)

Thank you