After upgrading vROPS from 8.18.3 HF5 to 8.18.5 using vRealize_Operations_Manager_With_CP-8.14.x-to-8.18.5.24967113.pak. You can no longer access the admin page. There is no HTTP error it just puts you on a landing page.
vROPS 8.18.5
The resolution was to restore the appliance to the latest snapshot and install the patch again. After this it came up properly.