Logic Pro X hangs for several seconds before recording - no overload message but max disk I/O meter

Hey All,

I'm running Logic Pro 10.2.1 on Yosemite (10.10.5) off a Late 2013 Mac Pro (new trashcan model) and was previously running Logic 10.1.1 on Mavericks with no issues until a few weeks ago. As I'll explain below, the issue hasn't gone away despite copious troubleshooting, so we upgraded in the hopes that it might help fix the problem (plus it's good to move up anyway, I suppose.)

When trying to record any audio file (one track or twenty, though I'm really only recording one thing at a time) Logic will start just fine, but after the completion of the first recording, it will show a Maxed out Disk I/O meter, and wait for a few seconds before looping (if I'm cycle recording) or running the next take. Sometimes it will even arbitrarily ignore a record command unless I hit stop twice before executing the next record command.

What's interesting is that I never get an overload message, or any overt error in Logic (no crashes or anything) it just seems like it's being stretched to it's limit when recording, which is clearly a big issue in any DAW.

I've tried literally everything I can think of - followed every step on Apple's troubleshooting and issues pages, read loads of discussion pages (the only one that really came close to helping me was this: Logic Pro hangs for 10-15 seconds when recording or playing where the person seemed to have the same issue, but theirs was resolved differently. They were recording to a Promise Pegasus which I have connected via Thunderbolt and use to keep samples and other large files, but I don't write to it and disconnecting it does nothing to fix the issue. I also do not have RAIDed drives though my internal SSD is partitioned 500GB to two drives, one the startup drive, and the other used for writing recordings to disk. Again, never had an issue like this ever.)

I've adjusted every option in Logic's preferences and project settings, all recording options, all latency options, all playback options, and absolutely nothing has fixed this issue.

Playing back, mixing, recording and playing back MIDI, creating automation, and all other major actions you can do in Logic are completely fine. None of them cause the Disk I/O meter to peak, and other than recording (arguably the most important part of this program) Logic is working perfectly well.

For the first time ever, I am completely stumped. Any ideas?