Maybe this is a feature and not a bug, but the Change event handler for selection components on Retool Mobile only fires after you make a second change to the component. The first selection from null -> selection doesn't trigger an linked event.
Thank you for bringing this to our attention. I tried testing this on my end and didn't quite see the behavior.
change_event_select_component.json (9.5 KB)
Here is a JSON copy of a mobile app where a change event on the select component triggers a JS query that returns a string. It seems to work as expected! Could you share a copy of your app or write into support so that we can take a look?