I would recommend opening a support case if this needs to be non-disruptive
Things you will need and they will probably request.
run config checker
verify RC file is correct
verify switch configuration (you already mentioned this)
Was failover successful before the upgrade?
In some cases I had to revert to the previous version of ONTAP and wait for problem to be resolved.
Maybe someone else can help on this forum but you would need to post basic filer configuration and version to go further.