I am in a similar situation. It is so annoying..They said they won't split! They asked for form of representative to be filled and l thought it's gonna happen. But two month past nothing has happened. I called IRCC, the agent told the officer put a note saying "waiting for BC"! Unrelated infor, Unrelated actions, no one is responding
Also did that a month ago, just regular respond saying "rest assured we're processing your application..."
They've not split the applications so far for the same reason you mentioned.
It sounds to me they hold the dependent's application as a hostage...

What can potentially go wrong with the principal applicant's background that would result in holding a dependent application?
It might be their laziness as they want to finalize the family together...