Yes, YouTube does not show all of your videos to your subscribers. The reason for this is the same of why Facebook, Instagram and now Twitter don't show you all of the content you follow on those platforms as well. When you follow 100's of people, they believe people will become overwhelmed because you're basically yelling in a crowded room with 100 other people yelling at the same time. That gets overwhelming for people and they won't spend as much time on that social network. They want to keep you on there as long as possible so they created an algorithim that looks at their viewing patterns and tailor to that.
The solution to this is two of them:
1. Now CTA the bell next to the subscribe button. Doing that will let them be notified on all new videos and content on YouTube you do.
2. Start to tailor your videos more to evergreen content so that way you'll always be finding new people who will subscribe and will continue to grow in views overtime.
You don't have to do evergreen content every time you upload, but if you want to continue to bring people in and keep views growing when your subscribers don't show, then i suggest doing more of that type of content.
