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In the Last Jedi, the Resistance, correctly assumes that

The First Order has a way of tracking them through hyperspace.

But why did they came to that conclusion, knowing that there is a technology that can signal your position across the entire galaxy?

Actually, Leia uses it so that Rey can find them

So why go straight to "a new technology has been developed" when the much simpler possibility "There is a tracker on one of our ships" (possibly hidden by a mole) was a valid possibility?

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  • It was, but if there was a mole, they would've found them sooner in TFA and shot them dead with Starkiller Base. Why would a mole appear in the 2-3 days between?
    – Edlothiad
    Jan 24 '18 at 12:16
  • Actually, only Ross, Finn and Poe jumped to the "a new tech" conclusion. We could reason that Leia, and later Holdo, both thought it's quite possible that someone on their side compromised their position. It explains why neither announced their exact plan until days later, at which point presumably they've ruled the possibility of a mole, or a tracking device, out.
    – Semaphore
    Jan 26 '18 at 10:17