Hi,
To understand, why it's only listing partial data is something that needs to investigated/reviewed on the monitoring tool.
If you notice similar symptoms or get similar errors when trying to fetch performance data within vCenter, you can apply the article. Please make a copy of the file before making any changes
It's only for datastores all other metrics return fine.
You can increasing mentioned the article to see if that helps.
Additionally, I was going through this article from Grafana where it says 'You should download as well the next Dashboards to have the full Hosts and Datastores visibility'.
VMware vSphere - Datastore dashboard for Grafana | Grafana Labs
Not sure if it's related, but worth checking