Our forms are taking a long time to come through via email or aren't appearing at all, why is this?

The past couple of weeks, our forms have been taking a while to come through (a couple of hours or longer), or haven't come through at all via email. We wondered why this is and how we can rectify it? 

Thank you in advance 

I did a test submission by adding my test email as the second recipient, and I received the submission instantly:

Most probably it was a temporary glitch, but could you please check and confirm if the issue persists?

We'll wait for your response.

Thank you!