Hoping for some help please. Each of our forms has at least 2 notifications that come through to us, usually with a PDF, but last couple of weeks usually only getting 1 per submitted form. The emailed notification goes to an Outlook account. We re-send but it can still take some time to arrive.
Is it a Outlook thing?
I would recommend you to take a look to the following documentation to understand how notifications are sent by WordPress, Gravity Forms basically compose the email according to your settings, but the sending process is done between WordPress and the server: Troubleshooting Notifications - Gravity Forms Documentation
Starting with Gravity Forms 2.4.15 you will see a note added to each entry, created with this version or newer, with the result for the notifications sending. So I would recommend you to go to the Entries list, click on any entry where you experienced the issue and scroll down to the Notes section to see the result, you can find an explanation for common results here: Troubleshooting Notifications - Gravity Forms Documentation