My understanding is that the law authorizing those student loans allows the executive to forgive the loans during a declared emergency. I'm sure the courts will sort it out.

I would hope if the courts are sorting this out they will put an injunction in place to prevent cancelling the debt until a disposition and all appeals have been exhausted, as that may be something rather difficult to undo.

They know it's going to get thrown out. But they also know that once the checks have been sent the courts can't do much to get the money back.

The court can issue an emergency injunction to prevent an irreversible action like that before the courts are finished with it. Considering the president can just keep postponing the debt there's no real rush here to complete the cancellation before the courts can rule on the constitutionality.