Hi Georgios,
Actually, you have found a very big error I made in the latest release and I hadn't noticed until now.
Expires header is an area that is very well covered in Webinoly, but during the latest update/release I was updating and adding support for some new file extensions. Now I see that some extensions were removed unintentionally.
# Old
location ~* \.(ogg|ogv|svg|svgz|eot|otf|woff|mp4|ttf|css|rss|atom|js|jpg|jpeg|gif|png|ico|zip|tgz|gz|rar|bz2|doc|xls|exe|ppt|tar|mid|midi|wav|bmp|rtf|swf)$ {
# New
location ~* \.(ogg|ogv|svg|svgz|eot|otf|woff|woff2|ttf|m4a|mp4|ttf|rss|atom|jpe?g|gif|cur|heic|png|tiff|ico|webm|mp3|aac|tgz|doc|xls|exe|ppt|tar|mid|midi|wav|bmp|rtf|swf|webp)$ {
# Now we need to "merge" both of them.
Sorry for the inconveniences and thanks a lot for reporting this issue.
It will be fixed in the next release v1.9.1 (this week).
Regards.