I'm currently developing for an embedded ARM devices running an opensshd v6.2p2. When an SSH connection was opened to this device (and held), I see

sshd[857]: dispatch_protocol_error: type 128 seq 507

messages every 10 seconds in the target's system log.

This doesn't happen with different SSH/SFTP clients.

I guess, the problem is in
void SshConnectionPrivate::sendKeepAlivePacket()
which is sending an SSH_MSG_INVALID (type 128) as keepalive. openssh's own ssh client is using SSH_MSG_IGNORE (type 2) for this purpose.

The issue is not critical as it doesn't affect the functionality, but the logs on the target system get quite messy, especially because QtCreator tries to keep the connection alive as long as possible.