gzip is not working properly: Text/HTML is disabled

I'm receiving this error message when enabling gzip compression -
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

mod_deflate is enabled on my server. gzip compression is enabled for javascript and css, but not for html... I'm not using any other plugins that alter the .htaccess file (the only enabled plugins I'm using are yours - smush, smartcrawl, dev dashboard and upfront builder).
This is my current .htaccess file:
# 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]
</IfModule>

# END WordPress
# BEGIN WP-HUMMINGBIRD-GZIP

<IfModule mod_deflate.c>

<IfModule mod_setenvif.c>

<IfModule mod_headers.c>

SetEnvIfNoCase ^(Accept-EncodXng|X-cept-Encoding|X{15}|~{15}|-{15})$ ^((gzip|deflate)\s*,?\s*)+|[X~-]{4,13}$ HAVE_Accept-Encoding

RequestHeader append Accept-Encoding "gzip,deflate" env=HAVE_Accept-Encoding

</IfModule>

</IfModule>

<IfModule mod_filter.c>

AddOutputFilterByType DEFLATE "application/atom+xml" \

"application/javascript" \

"application/json" \

"application/ld+json" \

"application/manifest+json" \

"application/rdf+xml" \

"application/rss+xml" \

"application/schema+json" \

"application/vnd.geo+json" \

"application/vnd.ms-fontobject" \

"application/x-font-ttf" \

"application/x-javascript" \

"application/x-web-app-manifest+json" \

"application/xhtml+xml" \

"application/xml" \

"font/eot" \

"font/opentype" \

"image/bmp" \

"image/svg+xml" \

"image/vnd.microsoft.icon" \

"image/x-icon" \

"text/cache-manifest" \

"text/css" \

"text/html" \

"text/javascript" \

"text/plain" \

"text/vcard" \

"text/vnd.rim.location.xloc" \

"text/vtt" \

"text/x-component" \

"text/x-cross-domain-policy" \

"text/xml"

</IfModule>

<IfModule mod_mime.c>

AddEncoding gzip svgz

</IfModule>

</IfModule>
# END WP-HUMMINGBIRD-GZIP