Was there a situation where an event ended up in a status it was not supposed to be in? Was there a mechanism that tracked status transitions and allowed or prohibited such a transition?

Yes, in complex state management systems, events sometimes transitioned into invalid statuses due to logical errors or data races. To prevent this, a control mechanism for transitions between statuses is often implemented — for example, a finite state machine. Such a mechanism explicitly defines allowed transitions and prohibits any others.

In Java, this can be implemented using an enum with transition check methods or with specialized libraries for finite automata. Here's a simple example of an enum with transition checks:

public enum EventStatus {
    NEW, PROCESSING, COMPLETED, FAILED;

    public boolean canTransitionTo(EventStatus next) {
        switch (this) {
            case NEW:
                return next == PROCESSING;
            case PROCESSING:
                return next == COMPLETED || next == FAILED;
            case COMPLETED:
            case FAILED:
                return false; // terminal statuses
            default:
                return false;
        }
    }
}

// Usage:
EventStatus current = EventStatus.NEW;
EventStatus next = EventStatus.PROCESSING;
if (current.canTransitionTo(next)) {
    current = next;
} else {
    throw new IllegalStateException("Invalid status transition");
}

This approach helps ensure the correctness of states and simplifies debugging.