Where to submit a bug?

The automated system isn't counting dead stones correctly.

Ref game:
https://www.littlegolem.net/jsp/game/game.jsp?gid=2418548

To me it looks like the AI-based auto score wasn't involved and all stones were just considered alive.

There is a contact link at the bottom left where you can message Richard.

Thanks, it's quite difficult to see on my system, the colors are too close.

There isn't an autoscore on this website. You need to mark the dead stones manually. There is a mechanism for not accepting your opponent's scoring (if they were the one to do the marking) but I don't remember exactly how that works.