I’m getting the same problem as wewie and schamane. I tried all the suggestions in the list.
I get the same error as schamane above. Any image uploaded after the 3.7.1 update doesn’t appear in the WordPress dashboard (only after clicking the image in Media Library and then Edit Image can I see the image.
I tried changing the permissions as schamane suggested and that worked, though I’m concerned about the safety of this.
My website is https://www.willbeck.com/ and the test post is from after the update.