I also have a feeling it's a hardware/software combination. All the post-Haswell Macbooks (from 2013 onwards) seem to fare much, much worse for audio applicatio

I also have a feeling it's a hardware/software combination. All the post-Haswell Macbooks (from 2013 onwards) seem to fare much, much worse for audio applications than the ones produced prior to the switch. I recently got rid of a late 2013 Retina MBP in favour of a late 2012 15" RMBP, and the difference in audio performance is astounding. No dropouts anymore, all my plugins work again, and Ableton is once again usable. I was hoping for a difference in performance but I was amazed at how much better the older one performed, with identical memory and SSD disk. And that's not the only issue I had with the 13" Haswell RMBP. Often it would lose its entire USB chain (which includes the built-in trackpad and keyboard!) which would require me to remote into it to shut it down. Thunderbolt wasn't much better, with frequent network dropouts over a gigabit tb adapter. The poor thing barely worked out of the box and it didn't get much better. I don't know what happened specifically with Haswell, but it seems like Apple and Intel haven't really been working to ensure it's a stable platform. It's a mess.