The number is currently hard coded. We limited it to prevent filling disk with unneccesary data. Normally you just need it to debug what went wrong so directly after print.
Anyhow, for next release you can relax it with a extra entry in the server startup config xml using:
<max-log-files-per-printer>10</max-log-files-per-printer>
See
https://www.repetier-server.com/startup-configuration/<br/>for more about the startup config and how to add your modifications correctly.