GUI lags on sample rates higher than 44kHz

I’m experiencing a very slow-responding GUI when working in projects with higher than 44kHz sample rates. I am now on a project that has 48 kHz sample rate, is a moderately dense proejct with a total of 75 channels including buses and fx channels. I’ve worked on bigger projects than this without the GUI lag on 44 kHz.

My system is iMac 3,7 gHz i7, 16GB 1333 mHz DDR3
Fireface 800

A friend of mine says he had this issue on both Cubase 8, 8.5 and 9 when using a Focursrite interface, but when using his UR28M interface he did not have the issue.

Does anyone have any suggestions to fixing this besides getting new gear?

Any difference if you increase latency? High sampling rates have lower latencies but use more resources, so it might be a good idea to increase the latency a bit.

I’ve tried. It doesn’t make any difference. Right now it’s at 2048…