We had the exact same issue with ClickSend a while back. Is the message you're trying to send bigger than 160 characters by any chance?
If so, you need to activate the 'message payload' option in the external account; this seems to be the only way to send multi-part messages with ClickSend through Adobe. This however has a big drawback : delivery receipts can't be sent back correctly to Adobe with this option actived, so any bounces won't be saved in Adobe; the delivery logs will all be set as 'sent' even though some had errors, and the 'billable sms count' will always be 1 sms per person, even if a single sms contains 8 messages (8*160chars).
We had a nightmare of a time with Adobe Support (more than 1 month and several calls !), where they were refusing to acknlowledge there was something wrong on their side with the way they read the delivery receipts, and ClickSend was saying the problem was with Adobe, so we just ended up switching provider and now everything works fine.
@cwammes In the logs that you've shared, it shows Send Status as "Stopped" and Canceled by User. Did you stop the delivery/ workflow by any chance? It does show "1 message waiting" before it is stopped. Additionally, check the sending logs (without stopping it) where it will show details of the message being sent.