Well, providing a link to that game would surely help…
I am assuming you mean this one: https://online-go.com/game/9632530
I am not connected to OGS developement in any way, but never have I heard about such a bug. Being a high level player I assume you know that after the game is finished both players need to accept the score and can click on groups to change their alive/death status? My best bet would be one of you accidentaly clicked somewhere and then you both accepted the wrong result.
Nevertheless contacting a moderator (by the convinient call moderator button on the right panel for example) should probably solve the issue.