I had the same issue, my lock file was not in /var/lock/apt-mirror, the apt-mirror was missing from /var/lock all together.
I found my lock file in /var/spool/apt-mirror/var/apt-mirror.lock. Once I removed the lock file apt-mirror was able to start once again.
I had the same issue, my lock file was not in /var/lock/ apt-mirror, the apt-mirror was missing from /var/lock all together. apt-mirror/ var/apt- mirror. lock. Once I removed the lock file apt-mirror was able to start once again.
I found my lock file in /var/spool/