Experiencing a similar issue.
I did find that if I open & save (nothing else required) my K2 categories and items they will THEN show up in the listings. Probably something to do with J! 1.7's new ACL.

There is probably an easy db query that can be run instead of manually opening and saving all items and categories (my site has thousands). I'll post again once I find an easier method.

Good news is that at first glance, after using jUpgrade, my K2 category and item IDs appear to be the same.

<<EDIT>>
Found the query, to make this quick.
In phpmyadmin run the following two queries. You will need to double check your new table prefix and adjust as necessary. Using jUpgrade the default is j17_

UPDATE j17_k2_categories SET access = '1' WHERE access = '0'
UPDATE j17_k2_items SET access = '1' WHERE access = '0'