Quote Originally Posted by Seleukus
Its because of a bug in the game - if you create enough client rulers, some of them will have the same name as each other, and the game can't differentiate between them, so when it tries to give the "Client Ruler" trait to your new client ruler, it gives it to an old one instead, and your new ruler isn't recognized as being one (hence the interloper trait.)

What I generally did in those circumstances was to replace the Type 4 government with a Type 3 government (using the process_cq cheat) to remove the interloper effects.
That seems strange, because that almost always has happened in my Pahlava campaign, and I only have three client rulers. Now whenever I try to create any more, they don't receive the client ruler trait, and are booted out of their settlements within turns of being installed.