Syniverse's importance in SMS was highlighted in November 2019 when a server failure caused over 168,000 messages to be delivered nearly nine months late. The messages were in a queue and left undelivered when a server failed on February 14, 2019, and finally reached their recipients in November when the server was reactivated.
We all just trust services like this... and mostly don't even know that/if we are using them, and assume them to be safe. It's always fun to learn about another service we should be skeptical of!