firebase deploy results in unexpected error - firebase

Question

Since yesterday, 'firebase deploy --only hosting' always results in an unexpected error when the uploading process is somewhere between 70 and 80%. But sometimes, it works after trying for multiple (~15x) times.
Any idea what my be wrong?
michaels-macbook-pro:dercampus michael$ firebase deploy --only hosting --debug -m "Updated Payment Logic"
[2017-12-01T00:29:57.404Z] ----------------------------------------------------------------------
[2017-12-01T00:29:57.410Z] Command: /usr/local/Cellar/node/8.6.0/bin/node /usr/local/bin/firebase deploy --only hosting --debug -m Updated Payment Logic
[2017-12-01T00:29:57.410Z] CLI Version: 3.15.4
[2017-12-01T00:29:57.410Z] Platform: darwin
[2017-12-01T00:29:57.411Z] Node Version: v8.6.0
[2017-12-01T00:29:57.413Z] Time: Fri Dec 01 2017 01:29:57 GMT+0100 (CET)
[2017-12-01T00:29:57.413Z] ----------------------------------------------------------------------
[2017-12-01T00:29:57.431Z] > command requires scopes: ["email","openid","https://www.googleapis.com/auth/cloudplatformprojects.readonly","https://www.googleapis.com/auth/firebase","https://www.googleapis.com/auth/cloud-platform"]
[2017-12-01T00:29:57.431Z] > authorizing via signed-in user
[2017-12-01T00:29:57.435Z] >>> HTTP REQUEST GET https://admin.firebase.com/v1/projects/XXXXX-******
Fri Dec 01 2017 01:29:57 GMT+0100 (CET)
[2017-12-01T00:29:58.178Z] <<< HTTP RESPONSE 200 server=nginx, date=Fri, 01 Dec 2017 00:29:58 GMT, content-type=application/json; charset=utf-8, content-length=116, connection=close, x-content-type-options=nosniff, strict-transport-security=max-age=31536000; includeSubdomains, cache-control=no-cache, no-store
[2017-12-01T00:29:58.180Z] >>> HTTP REQUEST GET https://admin.firebase.com/v1/database/XXXXX-******/tokens
Fri Dec 01 2017 01:29:58 GMT+0100 (CET)
[2017-12-01T00:29:58.791Z] <<< HTTP RESPONSE 200 server=nginx, date=Fri, 01 Dec 2017 00:29:58 GMT, content-type=application/json; charset=utf-8, content-length=266, connection=close, x-content-type-options=nosniff, strict-transport-security=max-age=31536000; includeSubdomains, cache-control=no-cache, no-store
=== Deploying to 'XXXXX-******'...
i deploying hosting
i hosting: preparing www directory for upload...
[2017-12-01T00:30:14.471Z] >>> HTTP REQUEST PUT https://deploy.firebase.com/v1/hosting/XXXXX-******/uploads/-L-ETiKmWtXToPJlS5vL?fileCount=32105&message=Updated%20Payment%20Logic
Fri Dec 01 2017 01:30:14 GMT+0100 (CET)
Uploading: [================================[39[32m= ] 79%[2017-12-01T00:32:44.879Z] <<< HTTP RESPONSE 409 server=nginx, date=Fri, 01 Dec 2017 00:32:44 GMT, content-type=application/json; charset=utf-8, content-length=82, connection=close, access-control-allow-origin=*, access-control-allow-methods=GET, PUT, POST, DELETE, OPTIONS, strict-transport-security=max-age=31556926; includeSubDomains; preload, x-content-type-options=nosniff
[2017-12-01T00:32:44.880Z] <<< HTTP RESPONSE BODY undefined
[2017-12-01T00:32:44.882Z] TypeError: Cannot read property 'error' of undefined
at module.exports (/usr/local/lib/node_modules/firebase-tools/lib/responseToError.js:10:12)
at Request._callback (/usr/local/lib/node_modules/firebase-tools/lib/api.js:43:25)
at Request.self.callback (/usr/local/lib/node_modules/firebase-tools/node_modules/request/request.js:186:22)
at emitTwo (events.js:125:13)
at Request.emit (events.js:213:7)
at Request.<anonymous> (/usr/local/lib/node_modules/firebase-tools/node_modules/request/request.js:1163:10)
at emitOne (events.js:115:13)
at Request.emit (events.js:210:7)
at IncomingMessage.<anonymous> (/usr/local/lib/node_modules/firebase-tools/node_modules/request/request.js:1085:12)
at Object.onceWrapper (events.js:314:30)
Error: An unexpected error has occurred.