Locust – AttributeError when accessing locust web interface

I’m trying to run a very basic locust load testing which did work previously.

from locust import HttpUser, between, task


class QuickstartUser(HttpUser):
    wait_time = between(1, 5)

    @task
    def get_status(self):
        self.client.get("/status/")

Running the following command: locust -f <package-name>/tests/load_tests.py -r 20 -u 400 -H http://localhost:8000 yields the following error message when trying to access the web interface:

[2022-12-28 23:23:30,962] MacBook-Pro.fritz.box/INFO/locust.main: Starting web interface at http://0.0.0.0:8089 (accepting connections from all network interfaces)
[2022-12-28 23:23:30,968] MacBook-Pro.fritz.box/INFO/locust.main: Starting Locust 2.14.0
Traceback (most recent call last):
  File "src/gevent/greenlet.py", line 906, in gevent._gevent_cgreenlet.Greenlet.run
  File "/Users/<user>/Coding/PycharmProjects/<project>-fastapi/.venv/lib/python3.10/site-packages/gevent/baseserver.py", line 34, in _handle_and_close_when_done
    return handle(*args_tuple)
  File "/Users/<user>/Coding/PycharmProjects/<project>-fastapi/.venv/lib/python3.10/site-packages/gevent/pywsgi.py", line 1577, in handle
    handler.handle()
  File "/Users/<user>/Coding/PycharmProjects/<project>-fastapi/.venv/lib/python3.10/site-packages/gevent/pywsgi.py", line 464, in handle
    result = self.handle_one_request()
  File "/Users/<user>/Coding/PycharmProjects/<project>-fastapi/.venv/lib/python3.10/site-packages/gevent/pywsgi.py", line 656, in handle_one_request
    if self.rfile.CLOSED:
AttributeError: '_io.BufferedReader' object has no attribute 'CLOSED'
2022-12-28T22:23:35Z <Greenlet at 0x106fbc3a0: _handle_and_close_when_done(<bound method WSGIServer.handle of <WSGIServer at , <bound method StreamServer.do_close of <WSGIServer, (<gevent._socket3.socket [closed] at 0x106fcb460 o)> failed with AttributeError

The following versions are being used:

$ poetry show locust --tree                                                       
locust 2.14.0 Developer friendly load testing framework
├── configargparse >=1.0
├── flask >=2.0.0
│   ├── click >=8.0 
│   │   └── colorama * 
│   ├── itsdangerous >=2.0 
│   ├── jinja2 >=3.0 
│   │   └── markupsafe >=2.0 
│   └── werkzeug >=2.2.2 
│       └── markupsafe >=2.1.1 (circular dependency aborted here)
├── flask-basicauth >=0.2.0
│   └── flask * 
│       ├── click >=8.0 
│       │   └── colorama * 
│       ├── itsdangerous >=2.0 
│       ├── jinja2 >=3.0 
│       │   └── markupsafe >=2.0 
│       └── werkzeug >=2.2.2 
│           └── markupsafe >=2.1.1 (circular dependency aborted here)
├── flask-cors >=3.0.10
│   ├── flask >=0.9 
│   │   ├── click >=8.0 
│   │   │   └── colorama * 
│   │   ├── itsdangerous >=2.0 
│   │   ├── jinja2 >=3.0 
│   │   │   └── markupsafe >=2.0 
│   │   └── werkzeug >=2.2.2 
│   │       └── markupsafe >=2.1.1 (circular dependency aborted here)
│   └── six * 
├── gevent >=20.12.1
│   ├── cffi >=1.12.2 
│   │   └── pycparser * 
│   ├── greenlet >=2.0.0 
│   ├── setuptools * 
│   ├── zope-event * 
│   │   └── setuptools * (circular dependency aborted here)
│   └── zope-interface * 
│       └── setuptools * (circular dependency aborted here)
├── geventhttpclient >=2.0.2
│   ├── brotli * 
│   ├── certifi * 
│   ├── gevent >=0.13 
│   │   ├── cffi >=1.12.2 
│   │   │   └── pycparser * 
│   │   ├── greenlet >=2.0.0 
│   │   ├── setuptools * 
│   │   ├── zope-event * 
│   │   │   └── setuptools * (circular dependency aborted here)
│   │   └── zope-interface * 
│   │       └── setuptools * (circular dependency aborted here)
│   └── six * 
├── msgpack >=0.6.2
├── psutil >=5.6.7
├── pywin32 *
├── pyzmq >=22.2.1,<23.0.0 || >23.0.0
│   ├── cffi * 
│   │   └── pycparser * 
│   └── py * 
├── requests >=2.23.0
│   ├── certifi >=2017.4.17 
│   ├── charset-normalizer >=2,<3 
│   ├── idna >=2.5,<4 
│   └── urllib3 >=1.21.1,<1.27 
├── roundrobin >=0.0.2
├── typing-extensions >=3.7.4.3
└── werkzeug >=2.0.0
    └── markupsafe >=2.1.1