after migrating to Apache Proxy Server, you *MUST NOT* use the RADSKMAN command to preload! -- RADSKMAN preload=... creates a folder/file structure for the Legacy-NVDKIT-based Proxy Cache which is not compatible with an Apache Proxy.
To preload an Apache Proxy Cache (applicable to Satellites only, not to a Core!) you have two options:
Select "Synchronize Satellite" in the Satellite Console (which will also initiate a Configuration Server DCS sync, if Configuration Server is enabled on this Satellite)
We have a DTM job scheduled to sync on a regular basis, but for the immediate syncs we either run it from Enterprise Manager or notify the server with this command:
nvdkit sync-server.tcl -metadata 0 -resources 1
This also works if you need to sync a full-service satellite. You can then change the metadata to 1 as well to get the data from the database, or change the resources to 0 if you don't want to sync the data files to the cache.