I have reported this issue for some time now and don’t understand why it’s not being addressed at this point. It seems many on this forum have noticed similar issues for some time now. When using Cubase 8 or 9 on the Mac OSX Mavericks (10.11.x) or Sierra (10.12.x), there is an incredible lag when working with Cubase whether it be selecting tracks, audio clips, resizing, zooming etc. I can confirm that this issue does not exist (or at least no where as bad) in Yosemite (10.10.x) and the same versions of Cubase. I have done extensive testing on multiple Mac computers (desktops & notebook) with various displays and hard drives (SSD & mechanical) and have been able to reproduce the same results every single time. Cubase 9.0.3 unbder the latest version of Sierra (10.12.6) has still not corrected this issue. Why? I had been told about a year ago that the development team in Germany was looking into the issue. Except, Mavericks and Sierra have been out for quite some time now, and soon to be replaced again. It shouldn’t take this long to solve such a problematic issue as this, especially when it effects the user working with the program. At some point soon, I will be forced to update the system and then have to make a choice if this is not corrected by then. I’ve been a long time Cubase user (along with many other apps on the market) and still prefer it’s workflow and options compare to the competitors, however, tings like this seriously need to be addressed. And I will repeat, this is an issue with Cubase under any Mac OS after Yosemite. So the issue did not always exist. And it’s reproducible on most Mac computers, especially the larger the project you’re working on. What’s worse is that I don’t believe Cubase 9 even officially supports Yosemite any longer (which it works much better on). I don’t really see how it could have been tested on the latest Mac OSX systems that it claims to support.
Yes, there seems to be many threads similar to this. But I haven’t found a single answer given for the cause of the problem as of yet. Nor the solution. Seems they need to determine what major changes were made from Yosemite to Mavericks that would cause such graphic issues. Possibly before High Sierra releases.
There was a thread for that. It’s been locked. I’m not sure why they did this, as the last couple of pages seemed fairly civil to me.
I’m optimistic, it is now marked as [CAN-6382] so hopefully they are getting closer to finding the cause and solving this.
Ha …I suggest you try Logic X and then see how lucky you have it.
I don’t notice any lag at all I’m on 10.11.
Cubase 9 GUI looks like a Ferrari compared to Logic X Model T.
Respectfully disagree about the appearance. I keep going back to Logic X (out of hate for the dongle), but always find Cubase at least a couple years ahead in both pro-level features and appearance. (For ex., Have fun with those skinny Logic X channel strips!) 
Though I really, really do hope SB can get mac performance back on track real soon. 
Sorry my comment may have confused you. I am not talking about the style of the GUI, I am referring to the performance of it.
From my experience on a 2013 MacBook Pro
Cubase = Ferrari = Fast = Good
Logic X = Model T = Slow = Bad