Hummingbird says "gzip is not working properly", how to fix it?

Hi there,

I've recently changed a few things on my Apache Server (WHM), basically implementing OPCache and FPM (FastCGI-Page-Manager) among other small things... And now the Hummingbird gives me this message. As there's a link for you at the end, here I am:

"gzip is not working properly:
- Your server may not have the "deflate" module enabled (mod_deflate for Apache, ngx_http_gzip_module for NGINX)
- Another plugin may be interfering with the configuration
If re-checking and restarting does not resolve, please check with your host or open a support ticket with us."

I've granted support access so maybe you guys can help me to find out what is going on. Thank you very much and have a good one!