Some alerts not received

We've recently experienced that some alerts for some alarms triggered from Grafana are not received in the xMatters app, while others are in the same period of time.

The screenshots below illustrates the following:

• The Alert inbox for the xMatters App on iOS
• Activity Stream for 2 alarms where alerts where received. Interestingly xMatters logs the failure: "Script failed with message: TypeError: Cannot read property "value" from undefined" for these alarms.
• Activity Stream for 2 alarms where alerts not where received

How do I track down why alerts are only received for some alarms?