>They're requesting in writing that no analysis was done, because then when they get the equipment back and see that yup, analysis was done, they can then I assume sue for... Something?

I'd assume if you're involved in a lawsuit against the police, and they make a factual claim like "we did not analyze items not listed in the warrant", that there's some sort of perjury type charge there.

While the police are allowed to lie to you, that's usually restricted to interrogations ("your partner has already flipped") not lying to the lawyer for the person suing you.