We have been seeing builds fail intermittently due to:
tar: debug/usr/bin: file changed as we read it
during the DebugSymbols build step.

One example from last night:
https://ci.chromium.org/p/chromeos/builds/b8944567408285318832
And two nights ago:
https://ci.chromium.org/p/chromeos/builds/b8944748795312710528

This has been happening for some time now, and seems to affect the cobblepot board more than others that we build, but for example it hit capri not too long ago:
https://ci.chromium.org/p/chromeos/builds/b8945023665389321616