I am working on bringing an older Joomla site (currently at 1.15.26) up to date, and last week I updated K2 from version 2.0 to 2.6.2.

After the upgrade all the articles are no longer being rendered on the main page (i haven't lost any data, it just will no longer show up where they were before).

Any advice would be greatly appreciated.

check the tips here
getk2.org/documentation/tips-a-tricks/item/311-manually-migrating-k2-content-from-joomla-15-to-17

Hello William,
Thank you for the quick response and the pointer to that tip article. Unfortunately I am not sure it applies since I am not moving from 1.5 to Joomla 1.7 (there is no new J1.7 Super User ID). This is 100% inside a single version of Joomla; 1.5.26.

I reviewed the instructions and changed the id of the created/modified user to someone else as well just to test. This did not fix my issue.

check the access also

The access was all set to public across the board already. I changed them to registered and back to public. The issue is still occurring.

When I switched the articles to registered the main page showed that there were no longer 40 pages of articles, and when i switched it back that page count returned.