Ceph dashboard throws "500 Internal Server Error" while collecting metrics.

Issue

• Ceph dashboard throws 500 Internal Server Error while collecting metrics.
• Manager logs shows ConnectionError: ('Connection aborted.', BadStatusLine(XXX))

2021-11-11 10:11:20.497 7fd1c673a700  0 mgr[dashboard] [11/Nov/2021:10:11:20] HTTP Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/cherrypy/_cprequest.py", line 656, in respond
    response.body = self.handler()
  File "/usr/lib/python2.7/site-packages/cherrypy/lib/encoding.py", line 188, in __call__
    self.body = self.oldhandler(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/cherrypy/_cptools.py", line 221, in wrap
    return self.newhandler(innerfunc, *args, **kwargs)
  File "/usr/share/ceph/mgr/dashboard/services/exception.py", line 88, in dashboard_exception_handler
    return handler(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/cherrypy/_cpdispatch.py", line 34, in __call__
    return self.callable(*self.args, **self.kwargs)
  File "/usr/share/ceph/mgr/dashboard/controllers/__init__.py", line 662, in inner
    ret = func(*args, **kwargs)
  File "/usr/share/ceph/mgr/dashboard/controllers/grafana.py", line 28, in validation
    response = grafana.url_validation(method, url)
  File "/usr/share/ceph/mgr/dashboard/grafana.py", line 21, in url_validation
    verify=Settings.GRAFANA_API_SSL_VERIFY)
  File "/usr/lib/python2.7/site-packages/requests/api.py", line 50, in request
    response = session.request(method=method, url=url, **kwargs)
  File "/usr/lib/python2.7/site-packages/requests/sessions.py", line 486, in request
    resp = self.send(prep, **send_kwargs)
  File "/usr/lib/python2.7/site-packages/requests/sessions.py", line 598, in send
    r = adapter.send(request, **kwargs)
  File "/usr/lib/python2.7/site-packages/requests/adapters.py", line 415, in send
    raise ConnectionError(err, request=request)
ConnectionError: ('Connection aborted.', BadStatusLine('\x15\x03\x01\x00\x02\x02\n',))

2021-11-11 10:11:20.497 7fd1c673a700  0 mgr[dashboard] [192.168.5.20:50302] [GET] [500] [0.009s] [admin] [513B] /api/grafana/validation/z99hzWtmk
2021-11-11 10:11:20.497 7fd1c673a700  0 mgr[dashboard] ['{"status": "500 Internal Server Error", "detail": "The server encountered an unexpected condition which prevented it from fulfilling the request.", "request_id": "209ce1e0-33fa-4b88-93ce-3e428525aeb8"}                                                                                                                                                                                                                                                                                                                        ']
2021-11-11 10:11:20.504 7fd1ec50c700  0 log_channel(cluster) log [DBG] : pgmap v2067814: 2944 pgs: 2944 active+clean; 3.8 TiB data, 29 TiB used, 404 TiB / 434 TiB avail; 1.5 MiB/s rd, 84 B/s wr, 1.58k op/s
2021-11-11 10:11:20.728 7fd1c4f37700  0 mgr[dashboard] frontend error (https://node2.example.com:8443/#/pool): Http failure response for https://node2.example.com:8443/api/grafana/validation/z99hzWtmk: 500 Internal Server Error
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