GZIP Compression not working


I have an issue with Hummingbird.
I can't get Hummingbird to perform a GZIP Compression. I keep getting the same error message:
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

I have turned off all plugins except Hummingbird and Woocommerce. I have changed theme to Storefront. I have made sure that my hosting supplier uses mod_deflate for Apache for the server my domain is on.
Still, I get the same error message.

Any ideas?