When watching a series and you're on one episode and the episode ends, there is no way to start the next episode. You have to go back to the episode list, wait for everything to load, scroll to the next episode and start playing it. EVERY other streaming app has a button to let you go to the next episode or they just start playing the next episode automatically.
Also, some series do not have all episodes available for free. On X1 you can filter to "Free for me" but not on the mobile app. There is no way to find which episodes are free, you have to click on each episode to see if you can play it or not.