1. Site Reviews does not officially support importing 3rd-party reviews (as mentioned above). The link provided above is for people who would like to try and do it on their own and it outlines the recommended steps to take.
If you installed the Updraft plugin (as it suggests in step 1), then you should be able to roll back your database to the point before you attempted to import the reviews.
I cannot really help you with this issue as there are too many other unknown factors in play that could be causing this. This is demonstrated by how it worked on one website, but you had issues on the other one.
Again, importing reviews is not officially supported, and the link provided is only if you would like to attempt it on your own.
2. Site Reviews already sorts reviews by date (latest to oldest). If this is not happening with your imported reviews, please verify that the format of the two date columns in the CSV file you used is correct and that it is not mixing up the day with the month on import (as explained in step 3).
You can also try sorting the CSV values by date before importing them, though if the format of the two date columns are correct, then this should not be a problem.