Gzip compression in HTML response works only sometime - apache

Question

I have a very annoying problem with my .htaccess. I saw it first time with the gzip compression but it affects Keep-alive and other things too.
The problem:
If I call the startpage of my website sometimes it gets the response as a compressed (gzip) version sometimes as a normal not compressed html.
(The transferred size of html sometimes is 9KB from 26KB sometimes 26KB from 26KB)
I tested it with different browsers and also with this online tool:
http://checkgzipcompression.com/
Sometimes it shows that I have compression active, sometimes it shows that it is disabled.
Here are some resouces
1) The good one (the response that I would expect all the time)
Accept-Ranges:bytes
Cache-Control:max-age=85419
Connection:keep-alive, close
Content-Encoding:gzip
Content-Length:8834
Content-Type:text/html
Date:Thu, 29 Oct 2015 10:59:55 GMT
ETag:"2282-5233bfba505e6"
Expires:Fri, 30 Oct 2015 10:43:35 GMT
Last-Modified:Thu, 29 Oct 2015 10:43:35 GMT
Server:Apache/2.4.10
Vary:Accept-Encoding,Host
2) The bad one: Response without keep-alive, Vary:Accept-Encoding, Content-Encoding
Cache-Control:max-age=85486
Connection:close
Content-Length:30347
Content-Type:text/html; charset=utf-8
Date:Thu, 29 Oct 2015 11:05:56 GMT
ETag:"e6fb558891db803ebcebd1b6aae83283"
Expires:Fri, 30 Oct 2015 10:50:42 GMT
Pragma:public
Server:Apache/2.4.10
X-Powered-By:PHP/5.3.28
3) And the ugly one: .htaccess (without redirects and rewrites)
### Begin: Browser caching of ressource files ###
# Enable long browser caching for JavaScript and CSS files.
# This affects Frontend and Backend and increases performance.
# You can also add other file extensions (like gif, png, jpg), if you want them to be longer cached, too.
<FilesMatch "\.(jpg|png|js|css)$">
<IfModule mod_expires.c>
ExpiresActive on
ExpiresDefault "access plus 7 days"
</IfModule>
FileETag MTime Size
</FilesMatch>
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType text/css "access plus 7 days"
ExpiresByType text/javascript "access plus 7 days"
ExpiresByType image/gif "access plus 1 year"
ExpiresByType image/jpeg "access plus 1 year"
ExpiresByType image/png "access plus 1 year"
ExpiresByType image/bmp "access plus 1 year"
ExpiresByType image/jpg "access plus 1 year"
ExpiresByType application/x-shockwave-flash "access plus 7 days"
ExpiresByType application/javascript "access plus 7 days"
ExpiresByType application/x-javascript "access plus 7 days"
ExpiresByType image/x-icon "access plus 1 year"
ExpiresByType application/x-font-woff "access plus 1 year"
</IfModule>
<IfModule mod_deflate.c>
<FilesMatch "\.(js|jpg|jpeg|gif|png|svg|css)$">
ExpiresActive on
ExpiresDefault "access plus 1 month"
SetOutputFilter DEFLATE
</FilesMatch>
</IfModule>
# BEGIN keep alive
<ifModule mod_headers.c>
<FilesMatch "\.(js|css|xml)$">
Header append Vary Accept-Encoding
</FilesMatch>
### Begin: Static File Cache (options) ####
# Set proper content type and encoding for gzipped html.
<FilesMatch "\.gz">
Header set Content-Encoding gzip
</FilesMatch>
# if there are same problems with ForceType, please try the AddType alternative
# Set proper content type gzipped html
<FilesMatch "\.html\.gz">
ForceType text/html
</FilesMatch>
<FilesMatch "\.xml\.gz">
ForceType text/xml
</FilesMatch>
<FilesMatch "\.rss\.gz">
ForceType text/xml
</FilesMatch>
### End: Static File Cache ###
Header set Connection keep-alive
</ifModule>
# END keep alive
### End: Browser caching of ressource files ###
Facts:
I have no LoadBalancing.
The same config is working like a charm on my local machine
The same .htaccess is working on the same server on a different VirtualHost (staging server)
(They could have slightly different php.ini)
How do I test it:
I simply pressing Crtl+F5 and experience response 1 and 2 randomly.