MongoDB ServerSelectionTimeoutError: No replica set members available for replica set name "abc"

I'm an experienced programmer, but a Python, Ubuntu, and Linux newbie. I apologize, as well, if this question would be better in a different forum.

I am working on a project in Python using PyCharm, with code executing in an Ubuntu environment in Vagrant. It has to access a MongoDb database.

When the database is local, I have no difficulties. I also can connect to one remote database. However, the database I most want to connect to is part of a replica set, and that seems to be the problem.

(I should say that the database with the replica set performs just fine in its actual role. I seem to be the one with the problem.)

We set up some ssh tunnels, using these suggestions:

Connecting to a Mongo Replica Set via SSH

We set up hosts and ifconfig appropriately.

My supervisor can now connect with minimal difficulty. I, however, keep getting this message:

pymongo.errors.ServerSelectionTimeoutError: No replica set members available for replica set name "abc"

The connection information includes all 3 replica set servers as part of the host string, plus the replica set name being specified and ReadPreference.PRIMARY.

The stack track looks like this:

File "/usr/local/src/dashboard/dashboard/dashboard/app/tasks/exports/__init__.py", line 95, in get_sections
    sections = CourseSection.objects(**params)
File "/apps/dashboard-env/lib/python3.4/site-packages/mongoengine/queryset/manager.py", line 37, in __get__
    queryset = queryset_class(owner, owner._get_collection())
File "/apps/dashboard-env/lib/python3.4/site-packages/mongoengine/document.py", line 198, in _get_collection
    cls.ensure_indexes()
File "/apps/dashboard-env/lib/python3.4/site-packages/mongoengine/document.py", line 878, in ensure_indexes
  collection.create_index(fields, background=background, **opts)
File "/apps/dashboard-env/lib/python3.4/site-packages/pymongo/collection.py", line 1753, in create_index
    self.__create_index(keys, kwargs, session, **cmd_options)
File "/apps/dashboard-env/lib/python3.4/site-packages/pymongo/collection.py", line 1641, in __create_index
    with self._socket_for_writes() as sock_info:
File "/apps/dashboard-env/lib/python3.4/site-packages/pymongo/collection.py", line 193, in _socket_for_writes
    return self.__database.client._socket_for_writes()
File "/apps/dashboard-env/lib/python3.4/site-packages/pymongo/mongo_client.py", line 965, in _socket_for_writes
    server = self._get_topology().select_server(writable_server_selector)
File "/apps/dashboard-env/lib/python3.4/site-packages/pymongo/topology.py", line 224, in select_server
    address))
File "/apps/dashboard-env/lib/python3.4/site-packages/pymongo/topology.py", line 183, in select_servers
    selector, server_timeout, address)
File "/apps/dashboard-env/lib/python3.4/site-packages/pymongo/topology.py", line 199, in _select_servers_loop
    self._error_message(selector))
pymongo.errors.ServerSelectionTimeoutError: No replica set members available for replica set name "abc"

The specific message No replica set members available for replica set name "abc" seems to be relatively uncommon, as I haven't found any hits on Google for problems with a specific named replica set.

Any suggestions would be much appreciated.