Average rating counts only last comment

Hi, I'm trying to use Komento as a testimonials page, only allowing guests to comment and using the average rating to 'show off'
For some reason the overall rating shown on the comments page only counts the last comment.
I think its the same bug like this guy had: https://stackideas.com/forums/don-t-know-is-it-s-a-bug-but
Support said this will be fixed in next release but unfortunatly it doesnt seem like it is.

First I thought Komento doesn't count ratings if they're from the same IP Adress, so I commented with my smartphone but that didn't work.
I think I fixed it by editing the comments.php model file, but I dont think this will last long because it might get overwritten by updates, right?
I commented out parts of the sql query in the comments model php -> Komento seems to give every comment a user id in the database in 'created_by' but since its all guests everyone has ID 0 so it only shows the last rating (created date). I checked this by changing one of the comments created_by value to a different number.
The page I'm testing this right now: http://neu.küchenprofis.de/erfahrungsberichte