In this case lets dig deeper.
Please check if there are .rrd files written at all. They should be in var/lib/openhab2/persistence/rrd4j
If there are files, delete them and see if it is working after that.
Checking the log files would help also.
For logging you would need to start the Karaf console and set:
log:set DEBUG org.openhab.persistence.rrd4j
If that doesn’t help we would look into the database using the REST API (the installation of the REST DOCS would be needed).
At a last resort and if nothing helps read Here. This user managed to get rrd4j working only after installing InfluxDB and Grafana. It doesn’t make sense to me but…