There's no way to create inconsistent transactions like this, the worst that could happen is that a locker signs a valid transaction that doesn't have time to be broadcast to the network.
What happens when lockers aren't available to sign for their allotted accounts?
Say we have 20 transactions from 20 accounts, being allocated to 20 lockers, and 10 of them are offline?
The accounts need to wait for the next round, if the transactions are not signed by the lockers they are invalid and won't be accepted by the network.