I spun up a clean install of Connections and CSV Import, downloaded the last file that was attached and imported it. I used the mapping shown in the screen capture (my best guess). The import did occur fine, all 265 imported. I did a spot check, randomly, 10% of them, and the data was correct. There is only one issue, and that was with the source CSV data, line 199, Rock B. Valley Yellow Pages, has an invalid date of 00/00/0000. This invalid date seems to throw PHP for a loop and stops the page load. This is why the select all didn’t work for you. The script never had an opportunity to load because of the error. After removing that date, the page did load fine. I suggest you edit the entry, it should be visible on the manage page, and remove the dates. After you do, the select all will work.
A valid date is checked for during import, invalids are supposed to be tossed. Not sure why this invalid date was permitted to import. I’ll have to check that in the morning and release a bug fix.
My suggestion … delete your data and do the import again. Make sure you have no filters set on the Connections : Manage admin page when you delete the existing entries.
My best guess is that all the entries were not deleted from any previous attempts to import a CSV file. That would account for duplicates. Also since you were mapping the ID to the Entry ID in previous attempts, that would also explain why you had mixed data in the entries (because of previously existing data which was not deleted).