sure!
during or after a conversation, anyone with the keys can create fake transcripts by creating messages with the same metadata, same nonce, different content.
because of this, no transcript can be proven to be the correct transcript. the trade-off is you don’t get forward secrecy on the per-message level, but you get it per-conversation.
another detail is that there is no identity, so all the above aside, there’s also no way to prove who sent which message.