I have integrated gmail-sync api into my backend service,

there are two operations which I perform WATCH where in I fetch 500 gmail’s from the registered account and store that data in the back-end.

another one is PUBSUB where in live emails are being watched the problem that I am facing I get an message_id representing an particular email now when I execute an fetch message data api where in with an particular message_id I can fetch all the data pertaining to it,
but in the case I some times get this error.

{
“error”: {
“code”: 404,
“message”: “Requested entity was not found.”,
“errors”: [
{
“message”: “Requested entity was not found.”,
“domain”: “global”,
“reason”: “notFound”
}
],
“status”: “NOT_FOUND”
}
}

All the message_id’s I am getting are from the pub/sub, not sure why it is causing the problem when details against that particular message_id is giving an 404, I am expecting 200 in most of the casees.