Sanboxes test is too strict - it expects sandboxes to be created immediately during upgrade. However, when new CNI files are placed on the node, new pods may not be able to start without throwing sandboxes errors. These pods start successfully later on. This test should ensure these kind of errors are marked as flakes if network/machine-config operators are progressing - and containers are created eventually.
Move to verified.
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 4.9.0 bug fix and security 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-2021:3759