Apparently a bug has been introduced in the latest Sierra update (10.12.4) which causes a USB audio connection, such as a USB connection to a DAC, to repeatedly fail, resulting in significant audio glitches. As a member of the Apple Developer program, I have some assurance (but of course am in no position to commit) that the bug will be fixed in the next release.
Some folks have reported the problem can be temporarily circumvented through use of un-powered USB hub. It would be best to hold off on the 10.12.4 update. But if you have already installed the update, the USB hub circumvention may work for you.
Update: Apple has released 10.12.5 which resolves the issue.