there is an php 7 warning in k2 filter: Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; plgContentJoomPlu has a deprecated constructor in plugins/content/joomplu/joomplu.php on line 26
caw plugins/content/joomplu/joomplu.php
Could you check again? as we don't have this kind of plugin.
that is your k2 filter component, module and plugin!!!
ok. it it not yours... sorry!
caw
You can contact its provider for help on this, I get this plugin uses old functions while your site is running with new PHP version which will notice deprecated methods like above.
Good luck!