Disclaimer: This a corner case and as such I doubt it deserves to be in the project’s documentation. However, someone might find this useful in future.
If you just switched to a distributed polling with RRDCached instance on separate host - you have to create the device folders structure within the <proj_root>/rrd directory for all existing devices on your web/primary instance. This won’t be needed going forward for new devices, it’s an ad-hoc operation. This is required for functions like the renamehost() which may fail with:
NOT renamed: Renaming of <DEVICE_NAME> failed