I assume that some of the members of the Cloudflare community are still having a problem when installing Cloudflare SSL. The general issue we encounter is we cannot log in with WordPress or it won’t respond.
The simplest way that I found how to fix it is to insert the code below on wp-config.php
if (_SERVER['HTTP_X_FORWARDED_PROTO'] == 'https') _SERVER[‘HTTPS’]=‘on’;
this should be installed above:/* That’s all, stop editing! Happy blogging. */
I hope this will help your issues regarding this matter.