I don't really know anything about this particular program. The problem is
encrypt with AES-256
is really under specified. Which mode of operation? Where does the IV/Nonce come from? How do they authenticate the ciphertexts? These are all important questions.
To find out we might try to look at their "specifications". The problem is: They do not answer all of those questions and the answers we get do not inspire a lot of confidence.
It starts with the fact that the first step is compression of the data. At least from a theoretical standpoint, that's a big nono.
Unless the files are repadded to a fixed length after compression (which would make it pointless) compressing the plaintext before encryption breaks any indististinguishability-based security notion for encryption, such as CPA or CCA security. This is because the size of the resulting ciphertext now leaks information about the file's content rather than just about the size.
It then adds unexplained 32 byte blocks before and after the plaintext before encrypting. This is rather weird, however together with the specification that they use CBC mode, a non-authenticated mode of operation, and do not specify the existence of a MAC anywhere leads me to the conclusion that they were trying to construct some kind of homebrew ad-hoc authentication mechanism. Probably comparing the decrypted first and last block after decryption.
This does not offer any kind of real authentication.
You can easily change parts of a CBC ciphertext without affecting the first and last block. (I'm sure they're going to argue that everything is fine because decompression might fail if I blindly change parts of the file. In general that's bollocks and there is no formal argument to support this!
This means that the ciphertexts are most likely not authenticated at all which means files in storage can be modified without you noticing when you decrypt.
Finally, they do not specify where the IV for the CBC-mode comes from. However this is crucial information, since the IV for CBC mode needs to be unpredictable, otherwise CBC-mode is completely broken. The fact that they do not realize that this would be an important part of the specification does not bode well.