ci-files01-hki is an internal webserver serving static files. It is used in provisioning scripts with the function "DownloadURL" in order to avoid downloading such files from external sources.
DownloadURL tries first to download from the internal server, and if that fails it tries the external one. If some request fails often, it is probably meant to be cached but has been forgotten or deleted.
This increases flakiness of the builds because of dependence to external resources.