Thank you for the reply.
I am the Google admin for the full organization that uses the Roku services. We have been using a single Gmail group as our publisher account email. This approach has worked for a few years now but stopped working a few weeks ago.
I checked all the emails that were blocked, filtered, marked as spam, etc., and there are no logs of any Roku service in the last month (I published new channels and opened new tickets with Roku Partner Success during that time period).
I have opened a ticket with Roku Partner Success about this matter several times now, but I have not received a relevant response.