serve() is called twice everytime I reload a blog page in wagtail

I am using wagtail to build a blog website. In order to count the visits of each blog, I override the get_context() and serve() to set cookie. The codes are as follows:

    def get_context(self, request):

        authorname=self.author.get_fullname_or_username()
        data = count_visits(request, self)

        context = super().get_context(request)
        
        context['client_ip'] = data['client_ip']
        context['location'] = data['location']
        context['total_hits'] = data['total_hits']
        context['total_visitors'] =data['total_vistors']
        context['cookie'] = data['cookie']
        context['author']=authorname
        return context
    
    def serve(self, request):
        context = self.get_context(request)
        print(request.COOKIES)
        template = self.get_template(request)
        
        response = render(request, template, context)
        response.set_cookie(context['cookie'], 'true', max_age=3000)
        return response

And the function count_visits is as follows:

def count_visits(request, obj):       
    data={}
    ct = ContentType.objects.get_for_model(obj)
    key = "%s_%s_read" % (ct.model, obj.pk)
    if not request.COOKIES.get(key):      
        blog_visit_count, created =BlogVisitNumber.objects.get_or_create(content_type=ct, object_id=obj.pk)
        blog_visit_count.count += 1
        blog_visit_count.save()

The problem I met is that when I reload the blog page, serve() was loaded twice. The first time request was with cookie info. But the second time the cookie of the request was {}, which caused the count of visit does not work correctly. I do not understand why serve() is called twice everytime I reload page. After adding a print command in serve(), the log of reload blog page is as follows:

[19/Sep/2022 23:08:44] "GET /notifications/api/unread_list/?max=5 HTTP/1.1" 200 38
{'csrftoken': 'vAnNLAp8Fb9zPkUOSrHTFGB5Bp4W4aLu8mQWPklIhX1JpDTcKIceeId03jTKJpA3', 'sessionid': '9qdgjulitvosan1twtqe0h5bpfn4z3hg', 'bloglistingpage_7_read': 'true', 'blogdetailpage_6_read': 'true'}
[19/Sep/2022 23:08:44] "GET /blog-1/ HTTP/1.1" 200 27594
{}
[19/Sep/2022 23:08:45] "GET /blog-1/ HTTP/1.1" 200 23783
[19/Sep/2022 23:08:46] "GET /notifications/api/unread_list/?max=5 HTTP/1.1" 200 38

And the log of curl is:

[19/Sep/2022 23:12:24] "GET /notifications/api/unread_list/?max=5 HTTP/1.1" 200 38
{}
[19/Sep/2022 23:12:29] "GET /blog-1/ HTTP/1.1" 200 23783