req.flash() data persists even after refreshing the page using connect-flash

Question

I am using connect-flash to have a flash message in my sailjs app. The flash message persists even after refreshing the page. I tried the solution on this

I created a policy to clear the req.session.flash array before any request but doing that shows no flash message any time. What's the correct way to show the flash message only once?

Edit :-

Code in my policy :-

        //removeFlash.js
        module.exports = async function(req, res, next) {
            req.session.flash = {};
            next();
        };

policies.js contains

'*' : 'removeFlash'

My controller contains

req.flash("error_msg", "Incorrect username or password."); return res.redirect("/login");