We have the same issue when mirroring Xenial repository since 2 or 3
weeks; we refresh our repository all hours, on odd hour it's working, on
even hour it's not working
Device or resource busy at /data/mirrors/env/usr/bin/debmirror line 2704.
releasing 1 pending lock... at
/usr/share/perl5/vendor_perl/LockFile/Simple.pm line 206.
Build step 'Execute shell' marked build as failure