I'm not a C# expert by any means. Is the IntegrityHash of the plaintext, and not the ciphertext? https://github.com/nrosvall/ylva/blob/2a4afcfb3727151fa09fdd...

That would be a really serious flaw. If not, hand rolled AES-CBC-SHA256.... why not just use an AEAD implementation? This is exactly why I look at these. There's a lot of nuance to that one decision, and so it usually gives quite a bit of signal about the project as a whole.