So I found a work around and not sure if this adds anything towards troubleshooting the issue.
I can get Lets Encrypt to work every time while I am downloading files. For example I will start 3, 2GB files downloading and then run the Lets Encrypt test and script and it will work and pass every time, so what the heck is that all about?
Sounds like your Dell SonicWall goes to sleep and blocks outbound requests when it is.
Forcing a download (inbound) request wakes it up automatically and thus outbound requests then work. Just a guess. Glad you found a work-around anyway. It is not a Let's Encrypt problem but one with your network reliability.