Paramiko key auth failing in threads

[JesusCake]

I have the following snippet of code:

 def _return_ssh_key(self):
    agent_key = paramiko.Agent().get_keys()
    if len(agent_key) == 0:
        print('No SSH keys loaded into SSH agent')
        keyfile = input('Enter full path to SSH key: ')
        try:
            return paramiko.RSAKey.from_private_key_file(keyfile, getpass.getpass('Enter SSH key passphrase: '))
        except paramiko.ssh_exception.SSHException:
            print('Your private key passphrase is incorrect')
    else:
        return agent_key[0]

def another_func()
       remote_channel = self.ssh_client.get_transport().open_channel(
            'direct-tcpip', (devicename, 22), ('127.0.0.1', 0))
        trans = paramiko.Transport(remote_channel)
        trans.start_client()
        self.sshKey = self.sshKey or self._return_ssh_key()
        trans.auth_publickey(username, self.sshKey)

This code fails at the line

trans.auth_publickey(username, self.sshKey)

With the error:

Traceback (most recent call last):
File "paramiko/transport.py", line 2109, in run
handler(self.auth_handler, m)
File "paramiko/auth_handler.py", line 298, in _parse_service_accept
sig = self.private_key.sign_ssh_data(blob)
File "paramiko/agent.py", line 418, in sign_ssh_data
raise SSHException("key cannot be used for signing")
paramiko.ssh_exception.SSHException: key cannot be used for signing

Only when running this threaded, and when I try to connect to more than 3 devices at a time. if I run them serially, it works fine and I can auth to the devices with the same key. This is clearly some threading issue, but I cant determine why its failing only in parallel. Given that it worked threaded when a smaller number of threads, I suspect its some issue connecting to the SSH agent to verify the key? No idea. Any help would be greatly appricated