I'm trying to put a vaadin-vertical-layout inside a popup-container, but ca

I’m trying to put a vaadin-vertical-layout inside a popup-container, but calling popup results in an error:

<vcf-popup id="popup" for="myComboBox">
    <template>
        <style>
            [part="container"]
 {
                background-color: green;
            }
        </style>
        <div part="container">
           <vaadin-vertical-layout id="popupContent"><span></span></vaadin-vertical-layout>
        </div>
    </template>
</vcf-popup>
[ERROR]
 2021-10-21 17:46:51,435 [http-nio-8099-exec-3]
 Attach existing element has failed because the client-side element is not found AttachTemplateChildRpcHandler.handleNode() (AttachTemplateChildRpcHandler.java:76)
[ERROR]
 2021-10-21 17:46:51,436 [http-nio-8099-exec-3]
  DefaultErrorHandler.error() (DefaultErrorHandler.java:34)
java.lang.IllegalStateException: The element with the tag name 'vaadin-vertical-layout' and id 'popupContent' was not found in the parent with id='261'
	at com.vaadin.flow.server.communication.rpc.AttachTemplateChildRpcHandler.handleNode(AttachTemplateChildRpcHandler.java:84)
	at com.vaadin.flow.server.communication.rpc.AbstractRpcInvocationHandler.handle(AbstractRpcInvocationHandler.java:66)
	at com.vaadin.flow.server.communication.ServerRpcHandler.handleInvocationData(ServerRpcHandler.java:412)
	at com.vaadin.flow.server.communication.ServerRpcHandler.lambda$handleInvocations$1(ServerRpcHandler.java:393)
	at java.util.ArrayList.forEach(ArrayList.java:1259)
...