Delayed/Broken Alarm Notification - when using Custom SMS Message

I am trying to send an SMS notification with a Sierra Wireless RV50x gateway device. I’ve followed the guide provided by IA, and believe the gateway is working correctly - I can consistently (tested many many times from a test tag) send notifications and receive them instantly so long as I’m using the default message from the notification block in the pipeline.

Using the same pipeline, and the same tag/alarm, when I fill in the SMS Custom Message in the alarm configuring on the tag, I either receive the messages much later or not at all. In some cases this was an hour later, sometimes 6-8 hours later, sometimes I never received them.

This particular pipeline has an email notification in parallel with the SMS notification, and it is worth noting that once the custom SMS message in the alarm has a value, the email notification shows the same behavior as the SMS messages leading me to think the issue is something between the tag and the alarm pipeline, not between Ignition and the RV50x.