I have been having similar issues when M1 sends me texts when an outdoor gate sensor is opened, and when it closes. I temporarily changed the email recipient from (my phone number)@vtext.com to (my Gmail username)@gmail.com. So far it is working reliably. I know it doesn’t explain why some of your text alerts seem to work on other zones, but so far for me it seems that sending emails via text is unreliable/delayed. I will continue to monitor. Ideally I would like texts versus emails as you probably do.