Ending a book in a series with a jaw-dropping cliffhanger comes with a risk, especially if the next episode isn’t yet available. There’s a fine line between leaving a reader intrigued versus frustrated. The latter may lose a potential fan.
If the sequel has been released, this is less risky. If not, and you absolutely want to end it that way, consider waiting to release the entire series at the same time. If the ending isn’t so abrupt that it drives readers crazy, then it’s not quite as hazardous to your fan base if they have to wait a while for the next episode.
However, there is nothing more disappointing to a reader than really getting attached to a great story that doesn’t have a satisfying ending. If there’s any doubt you’ll complete the story properly, especially within a reasonable amount of time, then avoid cliffhangers. Use a reasonable, albeit soft ending, you can pick up from later.