Hi mlambrecht,
I test this issue on my side. I create a custom picklist first, then add it to a custom entity, then create an app based on the custom entity.
Then I modify the custom picklist by adding a new item to it. On the app based on the entity, the newly added item won’t appear though I have refreshed the data source for several times.
Finally, I found out a way to show it. What I do is to delete the picklist on the entity first, then delete the custom picklist and create a new one. Then re-add the new picklist to the entity. On the app, refresh the data source, all the picklist items will be shown.
Please try if this will work for you.
Best regards,
Mabel Mao