The line that you indicate is in the function rule_match_post() which is matching an exact post and not a post ID. So somewhere on your site there is a location rule trying to match a post or this function would not be called. The value of the location rule is not set. Do you have field groups registered in PHP anywhere? Maybe in another plugin?
Welcome to the Advanced Custom Fields community forum.
Browse through ideas, snippets of code, questions and answers between fellow ACF users