OneAgent rotates logs automatically, plus there are rules for removing older logs so that a disk space is not taken needlessly.
In extreme circumstances, when free space becomes less than configured and an alert will be presented for the host, OneAgent will perform full cleanup. That means almost all its logs will be removed. Only installation logs remain plus the one log, which explains why the purge happend.
Could you specify what default values you are referring to?
We usually keep 5 files, which are at most 10 MB in size.
"Low disk space" threshold, when logs will be purged, can be configured through the UI for each host.
Click on host, click on edit, click on "Anomaly detection" and you can set thresholds for different events including low disk space.