Unlike a will, life insurance policies do not have to go through probate and aren’t subject to immediate judicial review.
A life insurance policy is a legally binding contract between the policyholder and the insurance provider. For a third party to gather adequate proof to establish that the named beneficiary is wrong is unusual, but legally possible.
Someone could contest beneficiary status on the grounds of significant life changes or a sudden change, such as if you change your policy at the end of your life. In addition, a person could build a case that you weren't of sound mind when naming your beneficiaries.