Citroën e-c3 2025 all backseat seat belt alarms went off with only 1 passenger

Hello,

I have an e-C3 since late 2025, when someone of normal weight sits in the back, all 3 seat belt alarms went off. Even if the person attached his seat belt, the other unoccupied seats still beeping so we ended up attached them all. No alarm went off if nobody in the back. And strangely enough, an overweight person sitting on the back didn't trigger any alarm, seat belt on or not.

Is this normal behavior or a known problem?