Graphs not showing any data

I followed server migration (https://docs.observium.org/server-migration/#prepare-new-server)
I have a problem with the devices cannot get any graph info in the new observium.
any troubleshooting steps to fix this problem?

Question I was asked by @adama
permissions
is the /opt/observium/rrd directory and all contents owned by the user that runs the poller?
chown -R observium.observium /opt/observium/rrd

I don't have a user with name "observium" in my new/old virtual machine. The /rdd directory recursively owned by root on both machines.