Not much else to say. if I had any idea why this is happening, I would have more. I must say that I am having way more issues with K2 than I ever did with vanilla Joomla. How can I uninstall K2 and return/transfer my items to Joomla articles?

1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')}' at line 1 SQL=SELECT `catid` FROM eo8l4_k2_additional_categories WHERE `itemID` = {intval()}

This is not related to K2.
An extension called K2 additional categories is causing this.

Please contact the extension's developer about this issue.

Excellent thank you.