Could you have your subs check the bell settings for that channel and see if they've opted-in to receive all notifications? They may be on the default setting, which is to receive notifications occasionally. Settings can be checked here: https://goo.gl/giVA8o
It's been going on for around 2 years now. They've recently opt it in for live streams which is another bad decision for the creators. They've got their reason for it but won't say why. And I guarantee it's not the "We think users may not want all of the feed" reason.