First take a look at all preferences with keyword "zebra", make sure zebra is enabled. Next, look at the cronjob in koha. Try with this command (for Debian) $sudo ps aux | grep zebrasrv   (or something like that) to check zebra index server is working on your server. Then look that the koha-common file in /etc/cron.d/koha-common ( you can search with command $locate koha-common) and check for right command crontab. (I'm using Koha packages installed on Ubuntu). If Zebra is not working, you can search for barcode with search the cataloge, but now with the title or name... Hope this can help!