XChacha20poly1305 vulnerability to known plaintext attacks
Using crypto_secretstream that should be fine. It generates a random nonce for each message. Reusing a key in that context is fine.

Original answer, before edit follows:

Yes, that's bad. You have to use a unique IV/nonce for each document.

A stream cipher, such as ChaCha, which is combined with the plaintext using XOR reveals the keystream to anyone who knows the plaintext. That allows them to decrypt other documents. And even if they do not know the plaintext, there can be attacks.

Every document has to have some unique identifier that you can use as a nonce. It does not have to be secret or unpredictable.