Posts relating for no reason

I have some posts with specific tags, but they appear randomly. And yes, the option “Relation based on” it’s selected “Tags”. For example: Post 1 have the tags “Post 2”, “Post 3” and “Post 5”, but “Post 4” appear here too, while in “Post 4”, which have tags “Post 2”, “Post 3” and “Post 5”, “Post 1” appears. Sorry for the confusion, it’s not my natural language, so any questions i’ll try answer, but please, help me. What sould i do?