This is all about HTTP headers: KLab now uses "integridd" header in SIF. Also, they use timestamp UTC header: this header i think that it includes a .md5 file. Between the data that this header sends with the score, this header has date & time data (timestamp UTC), so if you modify the score...
What i think about this is that KLab made the box/chest rewards server-sided with the maintenance they did to finish token event and put Aqours stuff in. The game client detects the score, yes, but the server won't validate it 100%: NO box rewards for you.
Kuroyama "fixed" the mod and the tester guy tried it: The mod now can bypass the transmission errors but the mod doesn't work at all, you won't get the chest rewards. As expected, KLab did a simple patch but very effective with this. I think the normal/whale players used this mod and with dummy...