We have 13k+ subscribers. New videos are not notifying to at least 100 out of 13k. I have checked notify subscribers in advance settings before publish a video, but same problem continues. Many times tweeted and mailed but no exact solution. Please help us @TeamYouTube
Thanks for the details. It'd be really helpful if we have a few example screenshots from your subs reporting they haven't received the notifications. Having said that, your subs can check their notification settings too: https://goo.gl/HQ5YxJ . Keep us posted.