Problem with Cloudflare and Magento 2

Hi everyone,
I have a strange problem with magento 2 and one of the good selling themes in themeforest. The problem is not present with default magento 2 theme.
When I am signed in to the store, it still shows me sign in button instead of sign out button. When I clear the magento 2 full page cache, the problem dissapears, but when I open the page from another browser with not signed in user and refresh the page on signed in browser it appears again.
After several days of investigation I have found that the problem is caused by Cloudflare, which I use also to manage that domain.
Turning on and off any feature in Cloudflare panel didn’t help. The only solution was to bypass Cloudflare from domain register.
I have tried different page rules, bypassing caching, security… and none of them helped.
What could cause that issue, because I want to use Cloudflare in front of my store.

regards

Have you already tried the official extension?

Do you have any CF app installed ?

Yes, I have installed that module and didn’t change anything.

I have removed all Cloudflare apps, enabled and disabled every Cloudflare feature and nothing helped.

Sounds like your theme is using a non standard way of using a resoource as a cookie which is cached by Cloudflare. You need to find that resource and prevent it from caching.

Can you give me some advice on how to proceed?

Consider this case: developer tries to retrieve a resource from server (i.e. a key) which is different on each request. For example resource url is: http://example.com/key.jpg which is not a static resource at server side (each request returns a unique content) and client is aware how to use that. But behind a service like CF that cause problem since CF will caches the result.

I still couldnt found a solution. Even with disabled security, performance, apps, cache level bypass, doesnt works as expected.
When I bypass from dns settings (make them gray) works fine.
What else can be checked?

PS
After reading that git Varnish cache issue with 'Sign In' link in header · Issue #9156 · magento/magento2 · GitHub second post, I found that when Cloudflare is on, X-Magenty-Vary cookie is missing.

At this point it might be best to file a support ticket so that one of our engineers can look at your specific configuration. Login to Cloudflare and then contact Cloudflare Support

Hi @ryan
I have opened a ticket 4 days ago but still no response.

I think I found your ticket. Let me see if I can get some eyes on it. The FREE queue has been quite busy this week.

7 8 days ago support requested HAR file, I have send it, but still no responce.

It looks like your Support Engineer got back to you early this morning. Looks like he’s working on another update. Stay tuned.

Hi was this problem resolved? I am also using Magento2 with Cloudflare and Ultimo from themeforest.