Regarding this topic that was solved and closed: https://piklist.com/support/topic/notice-trying-to-access-array-offset-on-value-of-type-bool/

I actually get the error again on another website. I have the latest Piklist and still get the error:
Notice: Trying to access array offset on value of type bool in /var/www/moumou.dk/cc/wp-content/plugins/piklist/includes/class-piklist-meta.php on line 126
If I change line 126 from
if(!is_null($meta_box['id']))
to
if($meta_box && !is_null($meta_box['id']))
It seems to work and throws no errors.