pgadmin4 exception: session['_id'] not in self.managers

I'm trying out pgadmin4 v2.0 for the first time. It seems that after only
a few minutes (maybe even less than five) my pgadmin4 session will get
logged out and I'll need to log in again and reopen everything from
scratch. This exception is thrown in the mod_wsgi logs:

mod_wsgi (pid=5965): Exception occurred processing WSGI script
'/home/pgadmin/venv/lib/python2.7/site-packages/pgadmin4/pgAdmin4.wsgi'.
Traceback (most recent call last):
File "/home/pgadmin/venv/local/lib/python2.7/site-packages/flask/app.py",
line 2000, in __call__
return self.wsgi_app(environ, start_response)
File "/home/pgadmin/venv/local/lib/python2.7/site-packages/flask/app.py",
line 1991, in wsgi_app
response = self.make_response(self.handle_exception(e))
File "/home/pgadmin/venv/local/lib/python2.7/site-packages/flask/app.py",
line 1567, in handle_exception
reraise(exc_type, exc_value, tb)
File "/home/pgadmin/venv/local/lib/python2.7/site-packages/flask/app.py",
line 1988, in wsgi_app
response = self.full_dispatch_request()
File "/home/pgadmin/venv/local/lib/python2.7/site-packages/flask/app.py",
line 1641, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/home/pgadmin/venv/local/lib/python2.7/site-packages/flask/app.py",
line 1544, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/home/pgadmin/venv/local/lib/python2.7/site-packages/flask/app.py",
line 1639, in full_dispatch_request
rv = self.dispatch_request()
File "/home/pgadmin/venv/local/lib/python2.7/site-packages/flask/app.py",
line 1625, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File
"/home/pgadmin/venv/local/lib/python2.7/site-packages/flask_login.py", line
792, in decorated_view
return func(*args, **kwargs)
File
"/home/pgadmin/venv/lib/python2.7/site-packages/pgadmin4/pgadmin/dashboard/__init__.py",
line 169, in wrap
kwargs['sid']
File
"/home/pgadmin/venv/lib/python2.7/site-packages/pgadmin4/pgadmin/utils/driver/psycopg2/__init__.py",
line 2000, in connection_manager
if session['_id'] not in self.managers:
File
"/home/pgadmin/venv/local/lib/python2.7/site-packages/werkzeug/local.py",
line 368, in <lambda>
__getitem__ = lambda x, i: x._get_current_object()[i]
KeyError: '_id'

My setup:
pgadmin4 v2.0 . The configuration is all defaults except
for LOG_FILE/SQLITE_PATH/SESSION_DB_PATH/STORAGE_DIR. That
means MAX_SESSION_IDLE_TIME is at its default of 60 (minutes).
pgadmin4 is in server mode with mod_wsgi as a host.
PostgreSQL 9.4.14 - from the postgres apt repository. No changes made to
timeouts or anything in the postgresql.conf , it's all defaults.
Python 2.7
psycopg2 2.7.3.1

I can confirm that the apache process hosting pgadmin4 is running under the
right UNIX user account and that it seems to have good access/permissions
to its scratch files on disk. I see updates being made to pgadmin4.db and
the sessions directory.

--
David Gilman
:DG<