Watching Gmail by Sender is Not Working

I am having an issue with a simple scenario where I want Gmail to watch for emails from sender “newsletters” and it is not producing any returns despite the fact that there is an email in my inbox that fits the description. I have made sure that I changed the start date to a date prior to the date of the email. It was working fine when I initially set it up two weeks ago but it has not worked since. Any ideas would be greatly appreciated…