WordPress 4.3 multisite image generate and resize issue

When I upload an image into the media library on a sub-site in our WordPress Multisite only the original image is uploaded. The smaller images could not be uploaded.

I have done the following:

• Map and file rights to 777, would not solve the problem
• Imagic is installed on the server (version 3.1.2)
• GD Library also installed (version 2.6.0)

Thanks a lot for your help!