After uninstalling a patch, problems were seen due to missing files. For example, Forms were not loading in Service Catalog.
Release : 17.2
Component : CA SERVICE CATALOG
The REPLACED folder in %USM_HOME% had been deleted at a previous date, so the files present in it would not show up on security scans.
However, when an uninstall of a patch is performed, it deletes the files that patch installed, then restores any files that were in the relevant subfolder of the REPLACED folder. With those files missing, no replacements were restored, and so the product hit failures on the missing files.