OVN has always had a node-before-master upgrade strategy, where ovn-controller is kept compatible with SBDB schema and format changes for a couple versions. The expectation is that all ovn-controllers are updated first, and only when compatible ovn-controllers are running does ovn-northd get upgraded and potentially make incompatible database changes. If this strategy isn't followed (which is the case with OpenShift which upgrades masters first) then older ovn-controllers may not understand the new changes to SBDB and might not install those flows to OVS, leading to missing flows. The CNO should be changed to upgrade the ovn-kubernetes node daemonset first, and whne all nodes in the cluster have been updated, then upgrade the master pods.
https://issues.redhat.com/browse/SDN-1373
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory (Moderate: OpenShift Container Platform 4.7.0 security, bug fix, and enhancement update), and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHSA-2020:5633
*** Bug 1915970 has been marked as a duplicate of this bug. ***