What I found is that one wireless mouse I have somehow causes the keyboard to not work when I log into the Openbox session. The same mouse causes the same problem in Openbox in Debian Stretch (on a different computer). I can actually plug in a different mouse, log out of Openbox, log back into Openbox, and then the keyboard works fine. Also, once I’ve logged back in with the second mouse, I can switch back to the first mouse and the keyboard works for the rest of that session. Thanks to all who tried to help.