I am able to produce a 400 error in the harbour microserver using Bumblebee.

Steps to reproduce
Log into Bumblebee
Clock Account > Customize Settings

This will always generate a 400 error in production and sandbox.

Harbour log
'{
"_index": "cwl-2017.07.25",
"_type": "staging-harbour-gunicorn-access",
"_id": "33473306762962239674349576326991664007371653540561027072",
"_score": null,
"_source": {
"referer": "https://devui.adsabs.harvard.edu/",
"cookie": "_ga=GA1.2.709485480.1500295539; _gid=GA1.2.658179556.1500564738; session=.eJxFjs0KgkAURl8l7rqFmm0EF4UZBPeKMSHjRirHxvGnGBVR8d0TIVqexXe-M0GSadFIcFrdiS0keQrOBJsHOIDsZqDCPanCwCpWGPmK1KvH8dCjdxi45RcxO-bBOXRhXrYfoat7Ler2Z3s2OkvadyHqv9TCHY0keUWK2LXE6GQH3m0gdimQcZOPuHAqOSsleVLFjCoeuutB1wi9BoJp2jB_AamkPPM.DFjvJA.eKYblsemq3JoLdjNi5Lb5UbyEeM; _gat=1",
"request_method": "GET",
"authorization": "Bearer:GeIq3Ij7EsYxFPT927kdwhCNNdkFfLTn2v3OD59l",
"response_length": "60",
"protocol": "HTTP/1.1",
"request_time": 3982,
"URLpath": "/user",
"host": "65.112.8.197, 10.1.0.44, 10.1.1.156, 10.1.0.118",
"moment_this_happened": "2017-07-25T15:03:07.610Z",
"status_line": "GET /user HTTP/1.1",
"user_agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:54.0) Gecko/20100101 Firefox/54.0",
"status": 400,
"@id": "33473306762962239674349576326991664007371653540561027072",
"@timestamp": "2017-07-25T15:03:07.610Z",
"@message": ""65.112.8.197, 10.1.0.44, 10.1.1.156, 10.1.0.118" "[25/Jul/2017:15:03:06 +0000]" "GET /user HTTP/1.1" "GET" "/user" "" "HTTP/1.1" "400" "60" "https://devui.adsabs.harvard.edu/\" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:54.0) Gecko/20100101 Firefox/54.0" "3982" "_ga=GA1.2.709485480.1500295539; _gid=GA1.2.658179556.1500564738; session=.eJxFjs0KgkAURl8l7rqFmm0EF4UZBPeKMSHjRirHxvGnGBVR8d0TIVqexXe-M0GSadFIcFrdiS0keQrOBJsHOIDsZqDCPanCwCpWGPmK1KvH8dCjdxi45RcxO-bBOXRhXrYfoat7Ler2Z3s2OkvadyHqv9TCHY0keUWK2LXE6GQH3m0gdimQcZOPuHAqOSsleVLFjCoeuutB1wi9BoJp2jB_AamkPPM.DFjvJA.eKYblsemq3JoLdjNi5Lb5UbyEeM; _gat=1" "Bearer:GeIq3Ij7EsYxFPT927kdwhCNNdkFfLTn2v3OD59l"",
"@owner": "084981688622",
"@log_group": "staging-harbour-gunicorn-access",
"@log_stream": "5a051c6cb3a3-gunicorn-access"
},
"fields": {
"@timestamp": [
1500994987610
]
},
"sort": [
1500994987610
]
}'

Api log
'{
"_index": "cwl-2017.07.25",
"_type": "staging-adsws-gunicorn-access",
"_id": "33473306766084344002143863567245356266442498648330797058",
"_score": null,
"_source": {
"referer": "https://devui.adsabs.harvard.edu/",
"cookie": "_ga=GA1.2.709485480.1500295539; _gid=GA1.2.658179556.1500564738; session=.eJxFjs0KgkAURl8l7rqFmm0EF4UZBPeKMSHjRirHxvGnGBVR8d0TIVqexXe-M0GSadFIcFrdiS0keQrOBJsHOIDsZqDCPanCwCpWGPmK1KvH8dCjdxi45RcxO-bBOXRhXrYfoat7Ler2Z3s2OkvadyHqv9TCHY0keUWK2LXE6GQH3m0gdimQcZOPuHAqOSsleVLFjCoeuutB1wi9BoJp2jB_AamkPPM.DFjvJA.eKYblsemq3JoLdjNi5Lb5UbyEeM; _gat=1",
"request_method": "GET",
"authorization": "Bearer:GeIq3Ij7EsYxFPT927kdwhCNNdkFfLTn2v3OD59l",
"response_length": "60",
"protocol": "HTTP/1.1",
"request_time": 41263,
"URLpath": "/harbour/user",
"host": "65.112.8.197, 10.1.0.44",
"moment_this_happened": "2017-07-25T15:03:07.750Z",
"status_line": "GET /v1/harbour/user HTTP/1.1",
"user_agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:54.0) Gecko/20100101 Firefox/54.0",
"status": 400,
"@id": "33473306766084344002143863567245356266442498648330797058",
"@timestamp": "2017-07-25T15:03:07.750Z",
"@message": ""65.112.8.197, 10.1.0.44" "[25/Jul/2017:15:03:07 +0000]" "GET /v1/harbour/user HTTP/1.1" "GET" "/harbour/user" "" "HTTP/1.1" "400" "60" "https://devui.adsabs.harvard.edu/\" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:54.0) Gecko/20100101 Firefox/54.0" "41263" "_ga=GA1.2.709485480.1500295539; _gid=GA1.2.658179556.1500564738; session=.eJxFjs0KgkAURl8l7rqFmm0EF4UZBPeKMSHjRirHxvGnGBVR8d0TIVqexXe-M0GSadFIcFrdiS0keQrOBJsHOIDsZqDCPanCwCpWGPmK1KvH8dCjdxi45RcxO-bBOXRhXrYfoat7Ler2Z3s2OkvadyHqv9TCHY0keUWK2LXE6GQH3m0gdimQcZOPuHAqOSsleVLFjCoeuutB1wi9BoJp2jB_AamkPPM.DFjvJA.eKYblsemq3JoLdjNi5Lb5UbyEeM; _gat=1" "Bearer:GeIq3Ij7EsYxFPT927kdwhCNNdkFfLTn2v3OD59l"",
"@owner": "084981688622",
"@log_group": "staging-adsws-gunicorn-access",
"@log_stream": "652b9daea486-gunicorn-access"
},
"fields": {
"@timestamp": [
1500994987750
]
},
"sort": [
1500994987750
]
}'

Both the harbour.app.staging.log and the harbour-service.staging.error.log have nothing for an error.

If this is not an error and just a response that the request found nothing, I would like it if we returned status 204 instead of 400.