pytube: [BUG] Empty streams for some videos

For some links, the streams property is empty, and the get_audio_only() method returns None. I’ve identified a few such links that seems to be reproducible. Here’s my test code that shows the problem:

from pytube import YouTube

FAILING = [
    "https://www.youtube.com/watch?v=L6nrMAFCzhg",
    "https://www.youtube.com/watch?v=T8de-31Hu7g",
    "https://www.youtube.com/watch?v=Y08HWyVSMxg",
    "https://www.youtube.com/watch?v=WchEW9LkK94",
]

OK = [
    "https://www.youtube.com/watch?v=7lYMmW2kPpQ",
    "https://www.youtube.com/watch?v=7eVQHt690nk",
    "https://www.youtube.com/watch?v=4bscOLDng0o",
]

for fail in FAILING:
    yt = YouTube(fail)
    stream = yt.streams.get_audio_only()

    # that's unexpected, stream shouldn't be None
    assert stream is None
    assert len(yt.streams) == 0

for ok in OK:
    yt = YouTube(ok)
    stream = yt.streams.get_audio_only()

    # same code, different links - all good
    assert stream is not None
    assert len(yt.streams) > 0

I’ve tested on freshly created virtualenv and the newest pytube. Same error on Windows and Ubuntu (WSL).