Is it possible to reverse Ansible vault data?
There are technically two ways:


brute-forcing your way to a valid passphrase
having a valid passphrase and using that to decrypt the data


The use of 256-bit AES is cryptographically sound as far as I can tell as a (cryptography) layperson, so there are no other ways.

That said, for Ansible vaults the way I have used them, you have to enter a passphrase. While the actual key is probably still derived from that passphrase, brute-forcing a passphrase may be easier than brute-forcing a lengthy key.

As for the two ways one thing can be encrypted using the same passphrase, this may be owed to salt. For example the current date and time may be part of the encrypted data and the actual vault data gets extracted from that.