Intermittent cancellation generating PDF with Browsershot

This is a followup to a previous thread, but with a new issue. In brief, the sequence outlined below goes without a hitch maybe half the time. But intermittently (in both Chrome and Firefox), the generate method below is listed as "cancelled" in dev tools, and returns back to the original page with the form that submits the post request. Inertia shows that form.wasSuccessful is false, but there are no errors. I've tried using callbacks on the submit() method, but they don't do or show anything.:

const submit = () => {
  console.log('at submit')
  form.post(route('auth.report.generate'), {
    onSuccess: () => console.log('success'),
    onError: () => alert("error"),
    onInvalid: () => alert("invalid"),
    onStart: () => console.log('start'),
    onCancel: () => alert("Cancelled")
  });
};

I'm not sure how to coax more information from inertia regarding the request cancellation. If there were a validation error, that should be showing up in the form object. In Dev Tools, I can see the payload of posted data for generate. The only other "clue" I've noticed is that the flash message (see below) appears on the original form page. Here is a more detailed description of what I am doing:

I have a form that uses useForm() and posts list of data items to a route pointing to a generate() controller method that 1) uses a form request to validate the posted data; 2) saves the posted pdf file name to the session; 3 sets the path to where the pdf will be saved; 3)saves the pdf with Browsershot; 5)redirects to an "success" inertia page that contains a link for viewing and downloading the pdf. The redirect also sets a success flash message for the success page to display.

//build `$data` array from posted data
$data[].....
// format: assembly-7-2022-47YzsWE.pdf
        $pdfFile = $data['report_file_name'];
        // save computed file name to session for use in showPdf()
        session(['districtPdfFile' => $pdfFile]);

        // /storage/app/public +file name
        $pdfPath = storage_path('app/public/'.$pdfFile);

        // html view of report
        $html = view('reports.pdf-report', $data)->render();

        // Generate pdf and save to /storage/app/public & /public/storage/
        Browsershot::html($html)->setNodeBinary(config('constants.node_bin').'node')->setNpmBinary(
            config('constants.node_bin').'npm'
          )->showBackground()->setOption('newHeadless', true)->savePdf($pdfPath);

        // redirect to success page, which contains link to showPdf() method to show/download pdf
        return redirect()->route('auth.report.success')->with([
          'message' => 'District or County Report generated successfully.'
        ]);

The link on the success page points to a controller method showPdf that retrieves the file name from the session and returns a response for viewing (and downloading) the pdf:

public function showPdf()
    {
        // NOTE: /storage/app/public and public/storage are symlinked

        // retrieve computed file name from session
        if (session('statewidePdfFile')) {
            $pdfFile = session('statewidePdfFile');
        } elseif (session('districtPdfFile')) {
            $pdfFile = session('districtPdfFile');
        } else {
            abort(404);
        }


        // check whether file is present in /storage/app/public
        if (Storage::disk('public')->exists($pdfFile)) {
            $filePath = Storage::disk('public')->path($pdfFile);

            // return file in browser as pdf
            // file can be downloaded from /public/storage
            return response()->file($filePath, [
              'Content-Type' => 'application/pdf',
              'Content-Disposition' => 'inline; filename="' . $pdfFile . '"'
            ]);
        } else {
            abort(404);
        }
  }