Thanks. Yes, disabling the Events Calendar Pro plugin, then re-enabling it, solved one issue: Now, all current and future events do show up.
The bad thing is that now the nice map view that used to be atop the listings, to show event locations, cannot be used. If I re-enable that view, or try to use any other view, such as Calendar or Grid view, the whole thing goes to pieces again.
This issue exists even after ALL other plugins have been deactivated. Therefore, I do not think there is any way for it to be a plugin conflict.
Thinking that it might be a corrupted file, I re-downloaded the Events Calendar and Events Calendar Pro plugin, and reinstalled them. That did not fix the problem of no longer being able to show anything other than the list view.
So, goodbye nice map and Calendar views, I guess.
Looks like maybe I might be having to find a different Events plugin. I went to Modern Tribe’s website and tried to get support on this issue, but they never responded.