Galaxy S9+: Message+ (6.6.4) Messages Randomly Not Delivered

[aarona62]

I upgraded to a Samsung Galaxy s9+ (from an S5) and noticed that since I have, my Message+ messages won't always deliver to the recipient. I have been in mid-conversation and notice a few times the conversation has abruptly stopped. In researching the message status, I see that the last response I had sent was not delivered. This is not always the case....most of the time my messages will be delivered.  Just randomly, a message is not. This has occurred with 4 different recipients (mostly Verizon users) over the past week since I got my new phone.  I used Message+ on my S5 as well, without issue.

Has anyone else experienced and resolved this issue?

Thank you in advance.