After playing a while (mostly deleting browser cookies and storage) I went to edge and it was working perfectly. Then I logged in on the site using edge, and same thing. So the issue seems to come from being logged. cookie or so… I forgot to mention I m using joomla
Needless to say, when I m greying out the proxy, the site works normally with no error at all in the logs
Before moving to Cloudflare, was your Joomla Website working over HTTPS connection?
Are there any possible firewall restrictions at your origin host/server?
May I ask what SSL option have you got selected under the SSL/TLS tab at Cloudflare dashboard for your domain ( Flexible, Full, Full Strict … )?
Here is a way to re-check if you correctly setup the SSL for your domain with Cloudflare:
In case you do not have an SSL certificate, you can use Cloudflare SSL, if so, kindly make sure you follow the instructions as follows on the below article to setup an SSL certificate using Cloudflare Origin CA Certificate:
Or send an an e-mail to support[at]cloudflare[dot]com from your e-mail associated with your Cloudflare account
Furthermore, if you have been through all these above suggestion and are not seeing corresponding issues on your network/server and you have a ticket number with Cloudflare, please reply and post that ticket number # here.
To enable efficient troubleshooting by support, please ensure you include the following on the ticket:
I got a notify of this post so ill try to help, i solved the 520 errors problem by disabling the cloudflare railgun, later on some of the administration panel was not working properly, it was because you have to set the website configuration directly in the nginx.conf and not in a different file.
Also 520 errors could come from, wrong permissions or php errors when it comes to nginx.
You want to make sure that your joomla installation has the proper user and 755 permission for folders and 644 for files.
So the solution should be:
Properly Config your Nginx.conf
Properly give permissions (755 for folders, 644 for files, user should he nginx)
Disable railgun on cloudflare (also try disabling rocket loader)
Try ignoring cache for administration panel url with cloudflare page rules.
Doing all of the above fixed both my joomla and my WordPress installations.