Cannot add items to existing appointments in production

[phinze]

Describe the bug
As an admin, trying to add an item to an existing appointment results in a validation error. Initial attempts to reproduce this in dev haven't panned out.

To Reproduce
Steps to reproduce the behavior:

1. Go to an existing appointment
2. Search for an item in the autocomplete box
3. Click "add item to appointment"
4. See error

Expected behavior
Item adds to the appointment and shows as the member having a hold on it.

[phinze]

Hm just made an appointment for myself in prod and I can add items to it just fine! 🙈

But we all watched this repro in our meeting... so going to have to figure out what the actual conditions for the bug are. 🔍