Hi there, @mmbay. Welcome to the Community! 
Have there been any structural changes made to the spreadsheet after it was connected to the Zap?
For example were any rows or columns deleted, was the worksheet sorted etc? You can learn more about the different types of changes that can affect the connection between the Zap and the spreadsheet here: Google Sheets error: Zap not triggering.
If that’s the case you’ll need to turn the Zap off and back on again to reset Zap’s the connect to the spreadsheet.
Can you give that a try and let me know if that gets it triggering?
Thank you! Turning it off and on again seemed to work.
Yay! That’s awesome news, @mmbay! 
Thanks so much for confirming that did the trick. Seems like you’re all set for the moment but please do reach back out to Community if you need help with anything else. In the meantime, happy Zapping! 