So weird. I had the same situation where everything was working. Then suddenly the notifications became sporadic. Then stopped pretty much altogether.
I did find a workaround, in case you can use it. I found that the only way I would receive emails is if the “To” address for the notification email had our website domain in it (in addition to the “from” address). So I went to my host and created a bunch of forwarding emails to use for this purpose. So the destination email I use in the form settings has our domain, but the emails actually forward to our personal addresses.
