CSRF token does not match - flask wtforms

Question

I'm trying to setup a very simple login form using flask wtforms.

For some reason I'm getting a validation exception

{'csrf_token': ['The CSRF tokens do not match.']}

Here's the html

<form method="POST" action="/login">
        {{ form.csrf_token }}
        <div class="login">
            {{wtf.form_field(form.username)}}
            {{wtf.form_field(form.password)}}
        </div>
        <input class="btn btn-primary" type="submit" value="login">

here's the relevant snippet

@app.route('/login', methods=["GET", "POST"])
def login():
form = LoginForm()
if request.method == 'POST':
    from itsdangerous import BadData, SignatureExpired, URLSafeTimedSerializer
    from flask import session
    app.logger.debug("Token in session")
    app.logger.debug(session['csrf_token'])
    from werkzeug.security import safe_str_cmp
    s = URLSafeTimedSerializer(app.secret_key, salt='wtf-csrf-token')
    token = s.loads(form.csrf_token.current_token, max_age=3600)
    app.logger.debug("Token calced")
    app.logger.debug(token)
    app.logger.debug("ret from safe_cmp = ")
    app.logger.debug(safe_str_cmp(session['csrf_token'],token))
    app.logger.debug(form.meta.csrf_context)
    app.logger.debug(form.meta.csrf_secret)
    app.logger.debug(form.csrf_token.current_token)
    app.logger.debug(app.secret_key)
app.logger.debug("login")
if form.validate_on_submit():
    # irrelevant login code
    login_user(user)
else:
    app.logger.debug("Validation error")
    app.logger.debug(form.errors) 

I've tried debugging wtforms to find the error, it looks like everything is ok from the logs and the tokens match..

I really have no idea why it fails as it seems to be the same token..

I've tried changing back and forth from form.csrf to form.hidden_tag(), have tried using the csrf class as described here https://flask-wtf.readthedocs.io/en/v0.12/csrf.html nothing seems to work.. Any help would be great..