[Bug] Downloading certain files suddenly doesn't work under iOS anymore

What I’m trying to do:

My app offers users APKG files (basically zip files) for download. Suddenly downloads under iOS start but never finish (stuck at 0%, 96% or even 99%) when you simply click on the link. It looks like this from the user perspective:

4 people independently reported this same issue to me. It started appearing in the last few weeks. I haven’t changed my code during that time and everything works fine on PC (Brave, Edge) and Android (Brave).

Weirdly enough, it also works when I offer a PDF file instead of an APKG for download.

Under iOS it only works when you long press the link and then choose “Verknüpfte Datei laden” (= “load connected file”).

What I’ve tried and what’s not working:

Here is my code that I haven’t touched recently (simplified, but enough to reproduce the issue):

Code Sample:

@anvil.server.http_endpoint("/test_dl/:")
def test_dl(**params): #✔️
  dl = app_tables.download_files.get(for_update=None)
  if dl is not None:
    r = anvil.server.HttpResponse()
    r.headers['content-disposition'] = 'attachment; filename="test.apkg"'
    r.headers['content-type']        = 'application/apkg'
    r.body = dl['anki_file']
    return r
  return "Fail"

Here you can try the download for yourself.