A yellow triangle to the left of the logged in user name at the top-right of the page shows the following error:
URL: https://server.fqdn/esa/ajax/common.search.route.RelatedItemsHandler/getData?searchCaseID=0.6.6283.2021729540&searchID=14124&previewFilter=&sc_obj=list_m%7C0~10~4~f&srr=1
Server exception: Error trying to serialize path: [ displayNameForDownload ]
There is a hung process that is no longer under control of the eDiscovery Job Manager which is preventing attachment retrieval.
Restart eDiscovery services on the case home of the affected case. In some instances, a server reboot is required.