As per the last comment from Jon, This issue happens for selective emails. And I can see a pattern in them. But still I am not sure if this is the cause.
I can see that this issue happens for mails when the label “UNREAD” is not in the list of labels in the json inside Gmail trigger node. I can observe this for 10 instances from the morning.
However I am not sure why a new email will not have a UNREAD tag. May be a bug from gmail api or downtime during the poll.
I believe “Unread” label must be applied by default for all the poll in n8n. Please let me know your thoughts. If you do not include Labels filter in the Gmail trigger node and send email to the connected gmail account continuously, say 1 email per minute to test, this issue can be reproduced.
Thank you for the response. I am doing that now. Just sharing this in the community, so that this can be a possible input for the dev team based on the last response for question # 23568. Thank you again for the workaround provided.