Can't edit the value of a pick list in my invoice

Can't edit the value of a pick list in my invoice

I have a custom field that I added to my invoices. For the last 2 years I have been able to hover my mouse over it and get the Edit link, which then allows me to choose a different value from the pick list.

Starting today, the edit link no longer shows up. It does show up on the other fields.

Why did this change? I hope it wasn't intentional.

Thanks!