This has been a bug for a really long time, guess it’s still not fixed. It has nothing to do with PlatformStand.
A workaround is to fire a RemoteEvent on the server that disables (and then quickly re-enables) the character’s Neck joint when the Died event fires on the client. This will force Died to fire on the server.
Also, if your character somehow moves after it dies on the client, then Died will also fire on the server. Disabling the Neck joint is more reliable, though.
Same issue with my ragdoll system but:
I fixed it with a reset button localscript that fires a remote on the server setting humanoid.PlatformStand to false and my player instantly died the moment i reset, works perfectly in the end.