I found another post describing "Show purchases in the iCloud". That described where to find this setting. In iTunes go to Preferences > Store. About half way down is the option Show iTunes in the Cloud purchases." This option was unchecked. After checking it, I clicked OK and then restarted iTunes. Now all my purchases have shown up again.
However sometimes this option doesn't show up:
You may need to restart iTunes. If that doesn't work sign out and sign back in to your account in iTunes and check if the preference shows up then. If that doesn't work there may be a problem with your billing. Fix that and check the preference again.
Update:
I saw a message today that said, "All of your movies are unchecked". And none of my content is showing up again and the preference, "Show iTunes in the Cloud purchases" is missing.
Restarting didn't help. Going to logout and log back in.