When attempting to access timesheets for users in the new UI, an error is thrown, and is noted in the app-ca log as well:
"ERROR 2018-10-04 13:16:44,393 [http-nio-6660-exec-3050] ppm.rest (clarity:ppmuser:24116951__11BD8468-70A9-42D6-BBA5-9A77DC63A0E0:PPM_REST_API) Error while loading attachments. attURL was null. Resource id"
The timesheets were not open for time entry. After opening the timesheets for time entry, the problem was resolved.