Just to confirm, is this happening for desktop, mobile or email notifications (or all of the above)? Does it show 'Subscribed' on the channel pages? Appreciate the additional info.
Thanks for the info. Please send a feedback report directly from YouTube with these steps for us to work on it: https://goo.gl/WdI0BK . While every individual report may not get a direct response, we do review everything and use the details to investigate and fix issues.