I don't think the problem will be in the submit which is outside the form. Since you are getting errors on the controls themselves or the form, I would look at how each is set. In the Form, check the DataSource, and item properties. In each data card, check the Data releated properties under the "advanced" tab.
Another thing to try is to create a new form from the same data source and see what properties are different for a given data card and it's UI control. Maybe powerapps thinks the UI control type doesn't the match the data soruce's fields so it throws these strange errors.
I suspect when it worked, you may have been working with a non refreshed data source change or a varibles that were already initialized and the error is actually elsewhere.
I would be curious to know what happens with a new form and if it differs or throws the same errors.