I recently switched from an old iMac 2012 to the new Mac mini 2018 (i5 6 core). I was very surprised (and annoyed) to find out that some of the FF plugins work much worse on the new system than on my old system. I have 10 instances of FF-R on a test project. Ableton shows about 50% CPU and cannot play w/o crackles. On my old system this was no problem.
It seems to affect FF-R and FF-L, but not FF-Q.
Somehow it seems to interfere with the graphics. The problem almost disappears when I minimize Ableton. Also the CPU usage goes down then (MacOS activity monitor). All plugin windows are closed during this test, btw.
I already tried to disable the graphic acceleration for FF plugins. But this did not help.
I know that the Mac mini has a crappy GPU (Intel 630). But I would not expect to see any interferences with audio plugins and their CPU usage.
I repeated this test with another VST/AU host (NI Maschine). Same problem.