Update: I got it it work in a different environment, so now I just need to figure out what the problem is with this one notification.

Hi Cindy! If all else fails, remove your recipient from groups and roles related to that table and assign them the table privs directly. There was a very old defect that had been resolved. Not sure if maybe you are seeing something related to it. DEF238214

Hey Garry! Thanks for the response. I tried sending to a user who was not a member of any groups or roles (and had full privileges to the table), but it still failed. I can see that the event is added to the TS_NotificationEvents table, but nothing in the Messages table.

It is working in Prod - so that's a plus, and makes it less critical, but it would be really nice to be able to test the changes before moving them up to Prod.

Cindy! Good to hear from you. Maybe we're missing something super basic. Do other notifications in this environment work? You mentioned it works in Prod, so maybe this environment isn't setup or maybe the notification service isn't running. 

Hi Vickie! Yes, other notifications in this environment work. It's only notifications from an aux table that don't. I tested from a different workflow/aux table in the same environment, and that didn't send either. It works in both Dev and Prod, but not Stage. So clearly it's environmental, but no idea what might be the issue. I've been poking at this thing for days. Now that we've determined it works in Prod, it's not such a big deal, but we'd still like to figure it out. I did submit a support ticket this morning.