For a moment, I was terrified* that I had accidentally deleted all 700+ photographs from a trip to Austria last year. Let that sink in for a moment - I will wait...
They were simply not in the directory of the Lightroom catalog so I started checking a backup and was relieved the find them safe and sound. Before I started a backup recovery, I followed a technical hunch that just maybe something funky was stopping Lightroom from displaying them. I "Quit Lightroom" and reopened it and there they were. I no longer try to explain these things. When it works it is pure magic. When it doesn't it is voodoo.
See ya soon,
*my level of terrified was limited to never telling a living soul that I had deleted them without a backup to recover from.