Problem with BP Time Attack Racer Ep. 6

I have followed the YouTube tutorial at BP Time Attack Racer: Checkpoint Functions & Testing | 06 | v4.8 Tutorial Series | Unreal Engine - YouTube until Episode 6. However, after I finished following until Episode 6 on Unreal Engine 4.25, once the player passed the first checkpoint in the right direction, the first checkpoint did not disappear and the second checkpoint did not get spawned. May I know why does this happen?