Please try these steps to help determine what process is modifying library.zip. These instructions are for Fedora but you can adapt them for Debian.
Install audit: sudo yum install audit.
Run the audit daemon: sudo systemctl enable auditd. You might need to also run sudo systemctl start auditd, in any case you can confirm if it’s running through ps -ef | grep auditd.
Set an audit watch on library.zip. Add the following lines to the end of the file /etc/audit/audit.rules. This is to ensure that the watch will persist on reboots:
# For insync
-w /usr/lib/insync/library.zip -p warx -k insync-lib
Add the watch to the current session: sudo auditctl -R /etc/audit/audit.rules.
When the issue happens again, run sudo ausearch -f /usr/lib/insync/library.zip -k insync-lib > library.zip.audit then send the library.zip.audit file.