/wp-admin/admin-ajax.php 403（禁止）

Question

I'm running WordPress on Windows server 2012 R2 in an Azure VM. In one of my sites, the theme options panel is not updating. When I check the console, I see that this error: /wp-admin/admin-ajax.php 403 (Forbidden).

The .htaccess file in the root folder looks like this:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
# Forbidding PHP files execution
<FilesMatch “\.(php|php\.)$”>
Order Allow,Deny
Deny from all
</FilesMatch>

# END WordPress

#GZIP Compression
AddOutputFilterByType DEFLATE text/plain
AddOutputFilterByType DEFLATE text/html
AddOutputFilterByType DEFLATE text/xml
AddOutputFilterByType DEFLATE text/css
AddOutputFilterByType DEFLATE application/xml
AddOutputFilterByType DEFLATE application/xhtml+xml
AddOutputFilterByType DEFLATE application/rss+xml
AddOutputFilterByType DEFLATE application/javascript
AddOutputFilterByType DEFLATE application/x-javascript

I've tried adding another .htaccess file into the wp-admin folder with the following:

<IfModule mod_security.c>
   SecFilterEngine Off
</IfModule>

But this does not work.

My permissions for the files are set like this: https://www.customfitonline.com/news/2013/6/20/solve-wordpress-on-windows-server-problems/

Any ideas on how to get this working???