Django renders an "in exception" page instead of a page that can help debugging

Django was working normally, suddenly I wasn't able to get any debugging messages. I have been commenting out my code to see which part is causing that and it turned out to be my last_visit middleware which gets when was the last time user visited the app. But why? what is wrong with it?!

last_visit.py (The middleware I made)

from django.http import HttpResponse
from django.utils.timezone import now
from django.contrib.auth import get_user_model
User = get_user_model()


class SetLastVisitMiddleware(object):
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        if request.user.is_authenticated:
            User.objects.filter(id=request.user.id).update(last_visit=now())
        return self.get_response(request)

    def process_exception(self, request, exception):
        return HttpResponse("in exception")

settings.py:

MIDDLEWARE = [
    ...
    'users.get_request.RequestMiddleware',
    'users.last_visit.SetLastVisitMiddleware'
]

from Django renders an "in exception" page instead of a page that can help debugging