Unexpected server error observed

create a user called comusr on ldap , with user roles as cluster admin
create two ldap groups called grp1 and grp2 with group roles as admin and cluster admin respectively
add comusr to grp1 and grp2
try to login on the UI using comusr as the username and password as password
expected: successfull log in
observed: the UI doesnt display any message and remains in the same page
the tail of debug.log of the corresponding node shows the following message:

[ns_server:error,2019-06-19T22:25:59.594-07:00,ns_1@cb.local:<0.24434.6>:menelaus_web:loop:163]Server error during processing: ["web request failed",

{path,"/uilogin"}

,

{method,'POST'}

,

{type,error}

,
{what,
{case_clause,
{"Administrator",
{auth,
[

{<<"plain">>, <<"fFbz3JyGM+awYQ3Xv3sFLCN0cl7Fw2UfTp0uGdF5NX+TYN4Y">>}

,
{<<"sha512">>,
{[

{<<"h">>, <<"EgDgbNof+TIzutPSVIw3iis4K8QszxTWnOl4uPctBt050jY7QraI4aMCodQKkVoGy8QJW4Y1+Iri7sEDDOR9ng==">>}

,

{<<"s">>, <<"mLydFwkwvvYiwCXEwDFqIAumgC5GAPgz0WCKWgNnl7aozqzLjvzc7KVgqCTVu07iJbPxkfMjD1AIQE+gS6D0WQ==">>}

,

{<<"i">>,4000}]}},
{<<"sha256">>,
{[{<<"h">>, <<"I78UJ7iS3AB1T5ILJBiKcwWjKfbzuNbmYo+xNjsDcgM=">>},
{<<"s">>, <<"lEJYJgAzMqDeSWoGF1fMnQtinll1v/TnO1qaqZtmf9Q=">>},
{<<"i">>,4000}

]}},
{<<"sha1">>,
{[

{<<"h">>, <<"UArODAdROECHSGs0N5DudFwS+Z4=">>}

,

{<<"s">>, <<"oYyDJ9CCQPNincSdZwUZt/islHs=">>}

,

{<<"i">>,4000}

]}}]}}}},
{trace,
[{ns_config_auth,authenticate_non_special,
2,
[

{file,"src/ns_config_auth.erl"},
{line,121}]},
{ns_config_auth,authenticate,2,
[{file,"src/ns_config_auth.erl"}

,

{line,103}

]},
{menelaus_auth,authenticate,1,
[

{file,"src/menelaus_auth.erl"},
{line,300}]},
{menelaus_auth,verify_login_creds,1,
[{file,"src/menelaus_auth.erl"}

,

{line,328}

]},
{menelaus_auth,uilogin,2,
[

{file,"src/menelaus_auth.erl"}

,

{line,360}

]},
{request_throttler,do_request,3,
[

{file,"src/request_throttler.erl"}

,

{line,59}

]},
{menelaus_web,loop,2,
[

{file,"src/menelaus_web.erl"}

,

{line,141}

]},
{mochiweb_http,headers,5,
[

{file, "/home/couchbase/jenkins/workspace/couchbase-server-unix/couchdb/src/mochiweb/mochiweb_http.erl"}

,

{line,94}

]}]}]