Why is angular complaining about duplicate keys for track expression?

I have the following angular template file that displays some team names, and I have this for loop inside an if directive:

@if (teams) {
    <p>Teams not null</p>
    @for (team of teams; track $index) {
        <app-name-box [name]="team"></app-name-box>
    }
}

This code is the template code for a component that I dynamically create multiple instances of, and is the only html code associated with the component. I assumed that anything inside the if would not get rendered if the if returns false. Only one of these components (the first one) has been given a value for teams, the others are given null, and I can see that because the "Teams not null" message only shows up in one of the instances of the component when dynamically duplicated. However, as I dynamically duplicate this component, I get the following error: The provided track expression resulted in duplicated keys for a given collection. Adjust the tracking expression such that it uniquely identifies all the items in the collection. Duplicated keys were: key "" at index "0" and "1".

As I duplicate this component, key "" at index "1" and "2", key "" at index "2" and "3" and so on are added to the list of duplicate keys, incrementing for every new instance created. I am struggling to understand why this is the case, since only one instance of this for loop should ever occur, so why are duplicate keys becoming a problem?

This does not seem to be a commonly reported issue, at least I have not been able to find much info about it so I had limited ideas as to how to try fix this. I did try using the *ngIf and *ngFor directives inside of the @ labelled ones but got the same result. I don't know what else I can even try, as I am not particularly experienced in Angular.

I am using Angular version 18.0.3 if that is relevant.

Turns out the issue was a malformed track expression in the parent component, despite the warning only being raised when the child component template was added. Either way, the warning message was completely useless.

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