So here's my scenario:
App.OnStart: ClearCollect(ProjectLists, dbo.ProjectView)
(Dropdown List)dlProjectList.Items: ProjectLists
When loading this in the app designer, everything seems to work fine. But when loading a published version for use, the dropdown will end up empty. This isn't 100% replicable, sometimes it works, sometimes it doesn't, but it seems like once it stops working it'll remain broken forever.
Turning off "Delayed Load" resolves this issue completely.
I'm not sure what Delayed Load does exactly, but my suspicion is that it's doing something like connecting the dropdown to the collection BEFORE the Collect runs in OnStart, because it's delaying the collection until "needed". I haven't verified if the collection ends up with data and the dropdown is empty, or if the collection is also empty.