Why is Canada struggling to revoke citizenship of 26/11 attacks mastermind Tahawwur Rana?

Canada is struggling to revoke citizenship of 26/11 Mumbai terror attacks mastermind Tahawwur Rana due to changes in legislation under former PM Justin Trudeau, which removed terrorism as a cause for such action. Authorities have been left with the option of attempting to prove that Rana obtained citizenship through deception. However, such revocations routinely take a decade to process.