Notice the error "file size changed while zipping"

Adding "delaycompress" might fix the issue.

rotating pattern: /var/log/zabbix/zabbix_server.log after 1 days (7 rotations)
empty log files are not rotated, old logs are removed
considering log /var/log/zabbix/zabbix_server.log
log needs rotating
rotating log /var/log/zabbix/zabbix_server.log, log->rotateCount is 7
dateext suffix '-20150715'
glob pattern '-[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]'
renaming /var/log/zabbix/zabbix_server.log.7.gz to /var/log/zabbix/zabbix_server.log.8.gz (rotatecount 7, logstart 1, i 7),
renaming /var/log/zabbix/zabbix_server.log.6.gz to /var/log/zabbix/zabbix_server.log.7.gz (rotatecount 7, logstart 1, i 6),
renaming /var/log/zabbix/zabbix_server.log.5.gz to /var/log/zabbix/zabbix_server.log.6.gz (rotatecount 7, logstart 1, i 5),
renaming /var/log/zabbix/zabbix_server.log.4.gz to /var/log/zabbix/zabbix_server.log.5.gz (rotatecount 7, logstart 1, i 4),
renaming /var/log/zabbix/zabbix_server.log.3.gz to /var/log/zabbix/zabbix_server.log.4.gz (rotatecount 7, logstart 1, i 3),
renaming /var/log/zabbix/zabbix_server.log.2.gz to /var/log/zabbix/zabbix_server.log.3.gz (rotatecount 7, logstart 1, i 2),
renaming /var/log/zabbix/zabbix_server.log.1.gz to /var/log/zabbix/zabbix_server.log.2.gz (rotatecount 7, logstart 1, i 1),
renaming /var/log/zabbix/zabbix_server.log.0.gz to /var/log/zabbix/zabbix_server.log.1.gz (rotatecount 7, logstart 1, i 0),
old log /var/log/zabbix/zabbix_server.log.0.gz does not exist
renaming /var/log/zabbix/zabbix_server.log to /var/log/zabbix/zabbix_server.log.1
creating new /var/log/zabbix/zabbix_server.log mode = 0640 uid = 102 gid = 104
compressing log with: /bin/gzip
gzip: stdin: file size changed while zipping
removing old log /var/log/zabbix/zabbix_server.log.8.gz