Picutre is gone after proxy is done.

I have a problem that occures at around minute 8 of my timeline. I imported a *.MTS-file (AVCHD) that is 10:39 minutes long, proxied it and when it's done, the picture in the viewer on the right hand sight is gone. Audio althoug is still good. During proxying I already cut the video. I first thought this was the problem so I renamed the imported video, imported it again and let it proxy.So now the untouched proxied video sits in my timeline and the picture is also gone. Any thoughts on that why this is happening? I already imported quite a couple of longer shots within this one project so this problem came out of nowhere.

Here is a screenshot: Screenshot @ ImgBB.com