Q: Where should I check to track this down?

Issue:

Opening a view model in my application sometimes makes dropdowns/datepickers nonfunctional.

ie. dropdown won't drop and the datepicker calendar won't come up

I suspect a binding issue but don't see one.

Dropdowns have normal things like strings, numbers.

One drop has a list of mini views.

Datepickers are bound to nullable dates set in the constructor of the viewmodel.

Note: These same things work in other viewmodels/views.

I can paste code, I'm just not sure what code is relevant here.