The FFU upgrade from 16.2.6 to 17.1.4 failed on a nested "name" found at:
/home/stack/overcloud-deploy/overcloud/config-download/overcloud/Controller/upgrade_tasks_step3.yaml (line 292)

Below the issue observed in the production environment:

2025-01-17 15:01:25.830613 | 566fdea1-0004-e53a-fb9d-000000000037 | FATAL | include_tasks | control0001-naz91 | error={"reason": "no module/action detected in task.\n\nThe error appears to be in '/home/stack/overcloud-deploy/overcloud/config-download/overcloud/Controller/upgrade_tasks_step3.yaml': line 292, column 3, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n - step|int == 3\n- name: Retag ovn_dbs container image\n ^ here\n"}

Looking at */home/stack/overcloud-deploy/overcloud/config-download/overcloud/Controller/upgrade_tasks_step3.yaml (line 292)* I can see a syntax error of nested "name" in task:

292 *- name: Retag ovn_dbs container image*
293 when:
294 - step|int == 3
295 *- name: Check for ovn_dbs retag statefile*
296 register: ovn_dbs_retag_state_file
297 stat:
298 path: /var/lib/tripleo/ovn_dbs_needs_retag
 

This issue seems today tracked and fixed at:
https://code.engineering.redhat.com/gerrit/c/openstack-tripleo-heat-templates/+/454509