Slow graphics on new Imac [Cubase 8.5]

Hi,
I recently bought a new Imac and installed my Cubase 8.5.3.
I noticed after installing few plugins on it (all legal) that the events\clips take time to respond when i move them across the timeline, as you can see in the video:

https://www.youtube.com/watch?v=tWLH_xvhcNM

After the event ‘sticks’ to the mouse curser it move normally, but when i release it and grab it again to move it, it take almost a second to ‘stick’ to the cursor ones again.

I noticed all the graphics are relatively slow.

What should I do? I’m completely new to mac so be specific :wink:

Thanks

imac specs:
Mac OS Sierra
Version 10.12.5
Processor 4.2 GHz Intel Core i7
Memory 16 GB 2400 MHz DDR4
Graphics Radeon Pro 580 8192 MB