I'm having an odd problem with audio engine dropouts, but only when looping a selection.  I'm mixing a simple project with only 13 tracks and minimal FX.  I'm using the latest version of Sonar Platinum (2016.05) with a Focusrite 18i20 with Mix Control 19.1b10 and 3.2.2 drivers.  My cpu usage is very low, and the file plays fine without dropouts until I try looping a section.  Then every time it rewinds to the beginning of the loop, I get an audio engine dropout.  I tried all of the buffer settings in the Focusrite driver, even up to 2048 and it still drops out.  I can play the file at 64 all the way through without looping a selection. 
 
I'm not trying to create a loop, I'm just playing a certain selection over and over to adjust EQ.  Can anyone suggest a solution?
 
Thanks.

Try increasing the I/O buffer size to 256 KB or 512 KB in
Preferences > Sync and Caching > File System.
 
 

+1  I would agree this is probably related to a disk-streaming bottleneck rather than CPU load. I would also recommend checking for problems with disk performance or interference from virus-scanning. I had a similar issue a while back when background scanning by Microsoft Security Essentials somehow got enabled.

Thanks guys!  Increasing the I/O buffer to 512 fixed it!