One way to understand how dripping works is by using the analogy of a house.
When you make something dripped, what you are doing is locking the door to that thing.
When you lock the door to something, you have to give someone the key in order for them to access it.
For example, if you give someone a key to a closet (a module in your course), but you haven't given them the key to the room it's in (the course itself), then they still can't access the closet (aka the module).
Or if you give someone the key to the closet and the lockable box, but the door to the house and the room are locked and you don't have the key, then good luck getting to the box!
So make sure that they are being given the "keys" to everything they need, which you give them through either triggers, automations, auto-responses, directly, or by putting it in the "content" of a product. See this guide for how to release access.
Note:
It's unnecessary for you to 'lock the doors' and drip something if it's already locked inside something else that you want people to access at the same time.
In other words, if you want people to access everything in a membership site once you give them the key to the membership site, then set the membership site to dripped, and everything else within it to published.
If you want people to access everything within a course once you give them access to the course, set the course to dripped, and the modules and lessons to published.