it is at least cruel and unexpected q.q
and where can you see the reason?

You can write a ticket and ask for the reason. When its an event room, you still have to do something like killing players, else its afk farming

that's how I played, it's just that the game stopped at a certain score so that the match didn't end before 8 minutes

Happens. There will be more events with 1000 zp+ rewards in the future.