A bug on the YouTube web site is telling users that the channels that they have subscribed to have not uploaded any videos yet. On mobile, though, everything is working fine. The issue has been fixed, but no information as to what caused the problem. There are no issues reported by YouTube on their Twitter account, but DownDetector has seen a huge surge in YouTube problem reports over the past few hours as can be seen by the graph below. Google has reached out to Google for questions about this issue.
Source: https://www.bleepingcomputer.com/news/google/youtube-web-site-subscriptions-are-broken-videos-not-displayed-fixed-/