Core K2 files were probably modified.
I'm looking now at the code and since there is no option to enable extra fields in the Latest items view you can't have them there. The workaround is to modify the check for it until we add an option for it (as part of a general option re-checking in K2).
First off, install v2.9.1 dev from:
github.com/getk2/k2/archive/master.zip
Then edit the file /components/com_k2/models/item.php and replace line 168 with this:
($item->params->get('genericItemExtraFields') && $view == 'itemlist' && ($task == 'search' || $task == 'date')) || $view == 'latest'
This should do it.
