Hi Douglas,
On looking at your system information and thinking through the nature of the error, I wonder if resolving this might be as simple as visiting the Events → Import → Import Settings tab and hitting the save button (you need not change anything).
Could you give that a go and then try manually importing an event one more time? If you still hit the same problem, can I ask you to again share a copy of your system information? Specifically, I’d be interested to know what the value of imported_post_status is at that point (which is contained in the sys info).
Thanks!