Currently, the ISOImporter reports unit download failures only via the progress report. It is requested that it also insert an error into the pulp.log indicating which unit couldn't be downloaded, and a reason.
https://github.com/pulp/pulp_rpm/pull/468
The fix for this bug is included in the 2.4.0-0.10.beta build that was just published to the Pulp fedorapeople.org repository.
verified [root@ibm-x3550m3-10 ~]# rpm -qa pulp-server pulp-server-2.4.0-0.21.beta.el6.noarch [root@ibm-x3550m3-10 ~]# Jun 25 21:31:28 ibm-x3550m3-10 pulp: nectar.downloaders.threaded:ERROR: Download of http://repos.fedorapeople.org/repos/pulp/pulp/demo_repos/test_repo_centos_comps_data/PULP_MANIFEST failed with code 404: Not Found Jun 25 21:31:28 ibm-x3550m3-10 pulp: pulp_rpm.plugins.importers.iso.sync:ERROR: Failed to download http://repos.fedorapeople.org/repos/pulp/pulp/demo_repos/test_repo_centos_comps_data/PULP_MANIFEST: Not Found.
This has been fixed in Pulp 2.4.0-1.