How is that possible? With 10000 transactions per second, you can never guarantee consistency like that. 'First' is relative when you're dealing with latency.
According to the paper, lockers are chosen at random anyway, so you've got the potential for different lockers to be signing the same spend in different rounds.
The claim of 20K TPS is on the global state, not per account. So account consistency is not really an issue for the locker.
We've previously replied about the way lockers from consecutive rounds communicate with each other to ensure account consistency.