I've been experiencing a similar problem. In my case, I was trying to
import a CSV file of only 244 records.
I'd get past steps 1 and 2 below. The progress bar would begin (and
console would show inserts happening) and then Sequel Pro would crash
somewhere around the 40th or 50th record. This happened over five
times in a row, even after I tried breaking the file into smaller sets
of records. Then finally, it just worked and imported the last 140 or
so records as normal.
I'm not sure if it's related or not, but when trying to import an SQL
dump from the production database into my local copy, I'm getting
crashes too.