Turbo.visit loading new page instead of loading turbo-frame

1

There have been other similar questions. But I cannot find one that has solved my issue. I am trying to load a turbo-frame using Turbo.visit. Here is the actual line:

Turbo.visit(myTargetUrl, { frame: 'mytargetframe' })

This causes my page to load myTargetUrl (instead of loading it into the frame).
In my before-fetch-request-event, the detail.fetchOptions portion of the event look like this:

{
    "fetchOptions": {
        "method": "GET",
        "credentials": "same-origin",
        "headers": {
            "Accept": "text/html, application/xhtml+xml"
        },
        "redirect": "follow",
        "body": null,
        "signal": {},
        "referrer": "https://apps.myserver.com/myapp/route1"
    },
    "url": "https://apps.myserver.com/myapp/route2/1234567890"
}

Note the presence of the referrer and the absence of a turbo-frame in the headers.
The target and srcElement values for that event are set to a long value that appears to be the content of my current page(?).

Now this code loads the frame properly so it is not something wrong with the naming or formatting of my frame:

$('#mytargetframe')[0].src = myTargetUrl;

The detail.fetchOptions for this before-fetch-event look like this:

{
    "fetchOptions": {
        "method": "GET",
        "credentials": "same-origin",
        "headers": {
            "Accept": "text/html, application/xhtml+xml",
            "Turbo-Frame": "mytargetframe"
        },
        "redirect": "follow",
        "body": null,
        "signal": {}
    },
    "url": "https://apps.myserver.com/myapp/route2/1234567890"
}

There is no referrer and the turbo frame is specified in the headers.
And the srcElement and target are set to:

turbo-frame#mytargetframe

What could be causing Turbo.visit not to work?

Thanks in advance.
John