In section 1.2.2 "ML2/OVS to ML2/OVN in-place migration scenarios that have not been validated" of the RHOSP 17 .1 migration guide, a bullet item references an issue that has been resolved:

- Delay the OVN migration until the issue is resolved. To monitor progress on the issue,
  see https://bugzilla.redhat.com/show_bug.cgi?id=2218596.