Flask flashing behaviour different in production compared with using flask development server

[hiven]

Flask delivers different results depending on whether deployed in production or in development, specifically around flashing messages.

This code fails to show the "something went wrong" flash in development but the same code shows the message in production.

@main_blueprint.route('/view/<items_id>', methods=['GET', 'POST'])
def view_items(items_id):
    item = Items.query.filter_by(id=items_id).first()
    if item:
        flash('Item List Ok')
        return render_template('main/item.html', item=item)
    else:
        flash('Something went wrong')
        return redirect(url_for('main.all_items'))

Code used:
https://github.com/hiven/FlaskApp

Environment:

Latest Flask version 2.2, python version 3.8