LogicException #403 - CSRF problem

Hey, sometimes i get a LogicException #403

LogicException #403 The action you requested is not allowed

error when i try to login. cant reproduce it reliable, it happend every week once i guess and is fixed after a reload ( the last few times it was right after a browser start with the login page as stored tab )

Login html :

PHP Code:

<?= form_open( base_admin_url() ) ?>
    <div class="input-field">
        <input type="text" name="username" size="45" <?php if( isset( $username ) ) echo 'value="', $username, '"'; ?> required />
        <label>Username</label>
    </div>
    <div class="input-field">
        <input type="password" name="password" size="72" <?php if( isset( $password ) ) echo 'value="', $password, '"'; ?> required />
        <label>Password</label>
    </div>
    <input class="btn" type="submit" value="Login" />
    </form> 


i do no redirect in the login check so i cant imangine how it can result in something like this

PHP Code:

// Your username and password should be periods not commas!

<?php if( isset( $username ) ) echo 'value="'.$username.'"'; ?>

<?php if( isset( $password ) ) echo 'value="'.$password.'"'; ?>

What did you Try? What did you Get? What did you Expect?

Joined CodeIgniter Community 2009.  ( Skype: insitfx )

yes, i know but it will not change the behaviour

i also noticed it in chrome and firefox ( didnt use/test edge often enoguh )

happend again - here is screenshot of the request