Lightroom Classic: Images will not fully render in Library module; only in Develop module

When going back to look through older folders, I noticed that Lightroom will not finish rendering images in the Library module.  In Grid mode, all the RAW files appear in their original, unedited state.  In Loupe view, the unedited image appears and has an infinite "Loading" message.  If I look at TIFF files, they appear as a severely pixellated image, with the same infinite "Loading" message.  The histogram also says "Calculating...".

As soon as I switch to Develop, the image renders as expected, and the histogram appears.

As I mentioned, this is happening in older images (whose previews have likely been deleted).  It does not appear to happen in a folder of images I'm currently working on (and have Smart Previews created for).

Actually, this seems to be happening for all of my images right now, not just older ones.

Using Lightroom Classic 7.3.1
OSX 10.13.4