In addition, I did two screenshots. This one shows that the featured image (Beitragsbild) is missing/has not been set after I saved it as a draft. It worked until 16:00 o'clock yesterday, then the plugin was automatically updated by WP and since then AFI does not work anymore.
This is the second screenshot, it shows up that the featured image is missing...
I did like you told me. Here comes the new log. I also deactivated, deleted (incl. settings), and reinstalled the plugin today. But it didn't help. Also, WP updated the plugin to 3.9.13, which also didn't make a difference.