You are using a custom init script running at cluster start to install a custom library. It works most of the time, but you encounter intermittent failures when apt-get update runs in the init script.
The failures return a Mirror sync in process error message.
Failed to fetch https://repos.<site>.com/zulu/deb/dists/stable/main/binary-amd64/by-hash/SHA512/<filename> File has unexpected size (228870 != 201863). Mirror sync in progress? File has unexpected size (228870 != 201863). Mirror sync in progress? [IP: 18.104.22.168 443]
This can happen if you are trying to download from a mirror that is not in sync with the main repository. Official repositories usually resolve the issue within 30 minutes, however in rare cases it can take much longer.
Wait for the mirror to finishing synchronizing with the repository before attempting to start your cluster.
Alternatively, if the library causing the failure is no longer needed, you can edit your init script to remove the reference to the problematic repo. You should only take this step if you are positive the library is not used directly or as a dependency.