In TLS 1.3 handshake protocol, the client sends the ClientHello message to the server. The server then sends back the ServerHello message followed by some encrypted messages. The client then computes keys and sends some other encrypted messages to the server to complete the handshake.
Now, what happens if an error occurs while the client is computing keys? Let's say it's an internal error. The client is supposed to send a fatal "Internal Error" alert to the server and then close the connection. The alert message is certainly not encrypted because the client does not successfully compute keys. However, the server already calculated keys successfully and changed cipher spec, so the server expects all incoming messages to be encrypted. Therefore, a decrypt error will occur when it tries to decrypt the unencrypted alert message from the client. Effectively, an internal error at the client becomes a decrypt error when it reaches the server. Is this an acceptable behavior?