I think you should be getting the notifications, but they can be hard to find!
(This is how you find them on desktop)
When you're logged in, look at the top right corner of the screen. Furthest to the left is your dashboard, then your profile picture. Click the icon directly to the left of the profile pic. After that you'll see a bunch of comics getting advertised and three options: gifts, messages, and activity. Click on Activity and you'll see all your notifications. If you click on them, they'll take you to the actual comment in the chapter. If you have a hard time finding the comments (because you get a lot of notifications from other things), you can filter to only see the notifications for comments.