Broken images in WordPress, showing on server!

Hi Guys!

First time here cause I really can’t get this fixed on my own I guess ??
The problem is that ‘suddenly’ some images are broken on my website (www.manify.nl).

The strange thing is that the images do exist on the server. Some images do work well. I checked the file permissions and ownership of the working and the non working images. They are the same. Just as the image extensions.

I Also did find some other posts talking about the .htaccess file, checked it and it didn\t solve the problem. Although it would be worth checking again if you guys have any idea ??

To start, I did deactivate all plugins and switched to the twentyfourteen theme to check if it was a theme or plugin based problem. I Also completely cleared and deactivated all caches (W3TC). The problem still exists.

Anyone an idea?!

Many, Many thanks in advance! All tips, tricks and help are more than welcome!