Wherever i placed your K2Filter_1.5.8_k2_2.7_J3.x_b0003 page gives me "Login first!" message.
Changed template and all categories and items are Public in K2.
Module is filtering without problem.
But this "Login first!" message is so persist.
Currently working on localhost. Joomla 3.9.24 / Joomla 3.9.23
K2 v2.10.2 / K2 v2.10.3 / K2 v2.10.4 (DEV)
PHP Version 7.3.12
Database Version 5.5.5-10.4.10-MariaDB
Web Server Apache/2.4.41 (Win64) PHP/7.3.12