@Christoffer Lindblom :

You can fix it by CSS :

Thank you. however it did now work. Any other ideas (see also the attached image)?

You need clear cache, i see it works :

I did clean the cache also on the server side (I use Sitground as the webhost). Hmm, I still see an "empty" thumbnails ... but I will let it pass some more time and check back later on. Good to see that it works for you

I will let you know ... and thank you for good support.

Now it works well?

Thanks for the follow up. I notice now that it works perfectly on FireFox and Opera ... but not in Chrome. Is this the same for you?