Here is an update, not sure it helps
The 2 email address that I was sending to both resided on Gmail. I created another account outside of Gmail, sent a test message 1 to the encrypted address, hosted by Gmail, the 2nd address not encrypted and outside of Gmail. Both were received
Sent yet another email to 3 addresses
1 encrypted, hosted by gmail
1 unencrypted, hosted by Gmail
1 unencrypted, hosted outside of Gmail
The 2 unencrypted email addresses received the message, the encrypted address did not receive the email
Looks like the problem only occurs when encrypted email is sent through Gmail and there is a mixture of encrypted and unencrypted addresses