Set Featured Image Not working?

Daniel and others, thank you so much for all your help thus far on this theme. I know I’m just a few tweaks away from having my blog be just the way I want it.

So, when I select “Set Featured Image” in individual blog posts (not the Header, as some “featured images” seem to be referring to) and if I choose to upload one (From Computer), I get a broken image gif. There’s a red star that I am led to believe SHOULD change into a green check when an appropriate title is entered, but it never does. I click “Use as Featured Image,” and it “works” in that it then posts a broken image at the top of my post. Fun tip: if I try to edit the image in the little modal, the image shows up, so I do know the upload “worked,” but again, as soon as I save, broken image.

I’ll try uploading from a URL, since I KNOW that’s at least online somewhere already. I enter the URL, and the red star turns to a green check. I try to enter the title, and again, red star stays as red star. There does not seem to be a place to select “Use as Featured Image.” I can’t tell if it would just pop up if the second red star turned to a check of if you just can’t do it via URL and it must be From Computer.

Is there a size limit that automatically “breaks” the image? Or is there something else interfering?

Thanks in advance!