Yes, kinda sorta.
I went into edit mode and looked at the posts where the image was clickable. I clicked on the image, and then on the "photo" icon that leads to the image editing screen. On each of them, on the first screen, "edit image". there was a URL in the space marked "link URL".
In the "edit image" screen of the unclickable images, that space was blank. However, if I moved over to "advanced settings", there was a URL in the space marked "Source". When I copied that URL and pasted it into the "link URL" space in the Edit Image screen, the image became clickable.
However, when you click on the image, you see it at the same size it was in the post, rather than at full size.
That solves the problem of the unclickable images, but not the problem of readers not being able to see the image full sized. Since my blog is mostly an art blog, I want my readers to be able to see detailed full sized images of the sketches and drawings I post.