A bit late on my reply, sorry. 🙂 I still have the issue, though. My work around is via deselecting the synth, Drummer or etc.... and it stops. These soft sun tracks also can not be frozen because they freeze always out of sync, which is a BIG drag. Thus, I have to bounce them in real time.
a) My clocking is internal, not via an outside source. b)There's a number of synths/vst and ARA that are not Silicon ready.
My CPU is fine, and I have 128g of Ram and lots of DSP via UAD. I work 90% of the time at 88K. My plugs and soft syn are stored on the main SSD drive.
So... There doesn't seem to be an answer to this issue - that I'm aware of. I've read other's having the same problem. IT's a REAL DRAG... my Mac Pro 2013 Intel, never had this freezing issue or gurgle sync issue when a soft syn is selected in a medium sized project. I don't run a mega number of tracks. My plugs aren't cracks... So! LOL... upgrading is not always an upgrade except for the retailer.