Well, got good news for you. I imported your file with zero issues. All 941 rows were imported. What I did, nothing, I chose the file and mapped the last name column in the CSV file to the last name field in Connections and mapped the combined named to the first name. It imported in roughly 10secs, pretty fast.
Since I had no trouble, I suspect it had to do with your mapping selections. Specifically require number 2 from the CSV File Setup Requirements.
I’ll do a second test import shortly after deleting these so I can test importing all columns from the CSV file.