Unhandled error during node learning: Traceback (most recent call last):
  File "/home/k/.local/share/virtualenvs/nucypher-iNjwDRsw/lib/python3.8/site-packages/twisted/internet/base.py", line 1283, in run
    self.mainLoop()
  File "/home/k/.local/share/virtualenvs/nucypher-iNjwDRsw/lib/python3.8/site-packages/twisted/internet/base.py", line 1292, in mainLoop
    self.runUntilCurrent()
  File "/home/k/.local/share/virtualenvs/nucypher-iNjwDRsw/lib/python3.8/site-packages/twisted/internet/base.py", line 913, in runUntilCurrent
    call.func(*call.args, **call.kw)
  File "/home/k/.local/share/virtualenvs/nucypher-iNjwDRsw/lib/python3.8/site-packages/twisted/internet/task.py", line 239, in __call__
    d = defer.maybeDeferred(self.f, *self.a, **self.kw)
--- <exception caught here> ---
  File "/home/k/.local/share/virtualenvs/nucypher-iNjwDRsw/lib/python3.8/site-packages/twisted/internet/defer.py", line 151, in maybeDeferred
    result = f(*args, **kw)
  File "/home/k/Git/nucypher/nucypher/network/nodes.py", line 626, in keep_learning_about_nodes
    self.learn_from_teacher_node(eager=False)
  File "/home/k/Git/nucypher/nucypher/network/nodes.py", line 808, in learn_from_teacher_node
    response = self.network_middleware.get_nodes_via_rest(node=current_teacher,
  File "/home/k/Git/nucypher/nucypher/network/middleware.py", line 260, in get_nodes_via_rest
    response = self.client.get(node_or_sprout=node,
  File "/home/k/Git/nucypher/nucypher/network/middleware.py", line 117, in method_wrapper
    host, node_certificate_filepath, http_client = self.verify_and_parse_node_or_host_and_port(node_or_sprout, host, port)
  File "/home/k/Git/nucypher/nucypher/network/middleware.py", line 66, in verify_and_parse_node_or_host_and_port
    node.verify_node(network_middleware_client=self)
  File "/home/k/Git/nucypher/nucypher/network/nodes.py", line 1214, in verify_node
    self.validate_metadata(registry=registry)
  File "/home/k/Git/nucypher/nucypher/network/nodes.py", line 1175, in validate_metadata
    self.validate_worker(registry=registry)
  File "/home/k/Git/nucypher/nucypher/network/nodes.py", line 1142, in validate_worker
    raise self.StampNotSigned
nucypher.network.nodes.StampNotSigned: 

Starting Learning Loop.
Cycled teachers; New teacher is (Ursula)⇀LightCoral Alembic PapayaWhip Airplane↽ (0xDF4927e39307514e6dE950952744C8B3f7f2c454)
Learning round 21.  Teacher: (Ursula)⇀GoldenRod Saturn MediumPurple Notes↽ (0xBb5A5Cc793B4a7d5C931E1585Bd9D25a9d71d381) knew about 10 nodes, 0 were new.