With small deployment, some validations are always failing.  In this case, collect-flavors-and-verify-profiles is failing :

(undercloud) [stack@undercloud-0-rhosp16 ~]$ openstack tripleo validator show history
+--------------------------------------+-------------------------------------+--------+-----------------------------+-------------+
| UUID                                 | Validations                         | Status | Execution at                | Duration    |
+--------------------------------------+-------------------------------------+--------+-----------------------------+-------------+
| cb96ffdd-8ffb-49b8-af77-881c1b0635e5 | 512e                                | PASSED | 2020-11-14T19:05:48.479781Z | 0:00:01.817 |
| 5ca1de3c-844c-4976-b70d-d854c533862d | dns                                 | FAILED | 2020-11-14T19:05:51.543026Z | 0:00:20.715 |
| 35676d70-0ca6-4248-b393-81fa5ddcc459 | service-status                      | PASSED | 2020-11-14T19:06:13.628661Z | 0:00:16.920 |
| 9058138d-5c9f-42c8-8273-d8d7b87176a3 | validate-selinux                    | PASSED | 2020-11-14T19:06:32.137655Z | 0:00:04.473 |
| 0179fd07-8893-475d-941a-5a3b98d99108 | ceilometerdb-size                   | PASSED | 2020-11-14T19:06:37.918709Z | 0:00:01.733 |
| e6854c8d-7929-4aa9-a7d3-fbe342907276 | ceph-ansible-installed              | PASSED | 2020-11-14T19:06:41.038911Z | 0:00:07.020 |
| 1ee1f27c-38ae-4596-9716-b14972e1be2e | tls-everywhere-pre-deployment       | FAILED | 2020-11-14T19:06:49.313886Z | 0:00:01.768 |
| 8d102809-a27a-4673-abab-4a6c83286e00 | ceph-dependencies-installed         | PASSED | 2020-11-14T19:06:52.315218Z | 0:00:13.521 |
| 018eed2f-e2a6-4c54-9999-3387c4f1738d | ceph-pg                             | FAILED | 2020-11-14T19:07:07.348151Z | 0:00:00.391 |
| fab0142d-fbe2-4ff8-b912-3d01a06eaa8c | collect-flavors-and-verify-profiles | FAILED | 2020-11-14T19:07:09.028188Z | 0:00:03.161 |
| 0b00d9b1-45f3-42d8-8e32-4722cc6dad4d | default-node-count                  | PASSED | 2020-11-14T19:07:13.495834Z | 0:00:05.705 |
| 16fcd5bc-80ee-42e3-90af-e0bd60cf37e8 | dhcp-provisioning                   | PASSED | 2020-11-14T19:07:20.416478Z | 0:00:06.842 |
| afecaa98-c7b0-488d-a711-7e8033acf5dc | undercloud-debug                    | PASSED | 2020-11-14T19:07:28.564627Z | 0:00:01.753 |
| aac6ab93-852d-4bed-83ee-1fc3ab57ae2e | ironic-boot-configuration           | PASSED | 2020-11-14T19:07:31.610433Z | 0:00:01.851 |
| a8e55be5-b087-4323-8dba-baaec64b3a88 | network-environment                 | PASSED | 2020-11-14T19:07:34.748073Z | 0:00:19.114 |
| 429fa314-2e3e-48d2-a8ab-1b20cc81ad6c | node-disks                          | PASSED | 2020-11-14T19:07:55.518984Z | 0:00:05.196 |
| 10e181e8-3db4-449a-a8e6-2786e8bf8fd5 | undercloud-heat-purge-deleted       | PASSED | 2020-11-14T19:08:02.140810Z | 0:00:02.387 |
| 7ade26f0-835b-4eff-9e4a-96125c3199f3 | switch-vlans                        | PASSED | 2020-11-14T19:08:05.830860Z | 0:00:20.115 |
| d9618e00-b449-45cf-b6f0-710db10c090f | undercloud-process-count            | PASSED | 2020-11-14T19:08:27.644715Z | 0:00:11.810 |
+--------------------------------------+-------------------------------------+--------+-----------------------------+-------------+


Version-Release number of selected component (if applicable):
Latest

How reproducible:
Always

Steps to Reproduce:
1.  Deploy a basic overcloud with 3 controllers, 2 computes
2.
3.

Actual results:
pre-deployment group consistently fails on some validations

Expected results:
no failures

Additional info: