Is ADS-B anonymous mode deterministic?
It is deterministic, meaning that if given exactly the same inputs, it will always produce the same output.

Your second question is whether it is reversible. The algorithm was deliberately designed to require an adversary to know the precise (i.e. within a few meters) latitude and longitude where the algorithm was run to be able to reverse it. This is effectively impossible unless they physically observe your exact startup location, in which case they could presumably just read your tail number off the side of your plane anyway.