Change site URL HTTP to HTTPS blank admin page

I’m using CloudFlare Flexible SSL function for a long time and I change to Full SSL today, the front end seems as normal but when I access wp-login.php it shows a blank page.

The SSL setting I changed before is Flexible SSL and the URL set as following:

Site URL: https://www.williamtai.moe
WordPress Home URL: https://www.williamtai.moe

I used WordPress HTTPS plugin and Rewrite rule to force all link to https connection.

Here is the write rule:

#Redirect to CloudFlare https
RewriteEngine on
RewriteCond %{HTTP:CF-Visitor} ‘”scheme”:”http”‘
RewriteRule ^(.*)$ https://www.williamtai.moe/$1 [L]

and now I changed the WordPress URL and Rewrite rule setting as following:
Site URL: https://www.williamtai.moe
WordPress Home URL: https://www.williamtai.moe

#Redirect for all
RewriteEngine on
RewriteCond %{SERVER_PORT} 80
RewriteRule ^(.*)$ https://www.williamtai.moe/$1 [R,L]

Now the front page is okay but the login page serve blank page.