Yes I had these problems sometimes myself.
That one thing was working and the next day it was not.
I had these troubles often with filters and lookup functions.
It seems as power apps is trying to reduce traffic, by loading only data Power Apps thinks that are really needed within the app.
It may help to explicilty refresh the datasource.
I never used choices as source for a dropdown.
Normally i hold all possible values in an self-created table, and use this datasource for the dropdown.
If you get troubles again with a choices it may be helpfull, to store the choices in a collection in the "On start" event. And than bind the combobox to that collection.
