Assuming you have a Collab-enabled project. Assuming your first initial publish has been done.

N.B.: Having a large amount of files helps reproduce this issue as it affords you more time/bandwidth to cancel at different moments and getting into different states.

1. Publish files
2. Cancel your publish

Notice that depending on the timing (potentially a server response issue) the client will display different messages:

* Operation cancelled (THIS IS THE RIGHT MESSAGE)
* Sorry, something went wrong (THIS IS THE WRONG MESSAGE)

Notes from Collab Deep Dive:
There seems to be an issue with how a Cancel during Publish is handled on the server end. It seems the server handles this as a 408 Request Time-out/Request Body Incomplete and the logs distinctly show several incongruous messages (the first one is good, the following ones not so much). The error body from the client logs show that the error handling seems to handle a 299 cancelled job as a generic "Sorry, something went wrong" when it should be "Operation cancelled".

2017-0328 14:44:07 GMT 740.845196 Collab Error *416932 71fa85a0917e5064598fd26c9d1b1343 JOB ERROR [CollabPublishAsyncJob] [Operation was cancelled] [FAILED] 9.115891s {"comment":"","revisionId":"","running":false,"waitingForCompletion":true,"progressType":2,"percentComplete":100.0,"totalCount":0,"currentCount":0,"completed":false,"cancelled":true} [Collab 2017-0328 14:44:07 GMT][Info] 'Operation was cancelled' (22) returned in 'C:\Development\Unity_Staging\Editor/Src/Collab/Jobs/CollabPublishAsyncJob.cpp' at line 361

2017-0328 14:44:07 GMT 740.845517 Collab Log *416932 71fa85a0917e5064598fd26c9d1b1343 JOB COMPLETE [CollabPublishAsyncJob] [Operation was cancelled] [FAILED] 9.116218s {"comment":"","revisionId":"","running":false,"waitingForCompletion":true,"progressType":2,"percentComplete":100.0,"totalCount":0,"currentCount":0,"completed":true,"cancelled":true}
2017-0328 14:44:09 GMT 742.756006 Collab Log *416932 482365e2f972eda418daf7f3c9e83c8d FUNC START [Collab::StartCollabJob] [] [] {"params":[{"newJob":"class CollabPublishAsyncJob"}]}
2017-0328 14:44:09 GMT 742.756216 Collab Log *416932 5104524a45ac10242932ca9dc172ee0c JOB NEW [CollabPublishAsyncJob] [] [OK] {"comment":"","revisionId":"","running":false,"waitingForCompletion":false,"progressType":2,"percentComplete":0.0,"totalCount":0,"currentCount":0,"completed":false,"cancelled":false}
2017-0328 14:44:09 GMT 742.757022 Collab Log *416932 482365e2f972eda418daf7f3c9e83c8d FUNC END [Collab::StartCollabJob] [] [] 0.000991s UPID Received '9c8799cb-8410-4625-a345-4128a4ecf2da'.

2017-0328 14:44:11 GMT 745.659722 Collab Log 450820 1d2af19e27c662447bcfeebd882d5c05 CURL NEW [UploadSignedURLsRequest] [] [] {"method":"PUT","responseHeaders":[],"uri":"https://collab.cloud.unity3d.com/api/projects/9c8799cb-8410-4625-a345-4128a4ecf2da/uploads/5b4cf688-99b8-4684-8c66-7decc2892bfc"}
2017-0328 14:44:14 GMT 748.103124 Collab Log *416932 5104524a45ac10242932ca9dc172ee0c JOB CANCEL [CollabPublishAsyncJob] [] [OK] 5.346919s {"comment":"","revisionId":"d24533a7e4720b7079386fac3d1b95fade40e584","running":true,"waitingForCompletion":false,"progressType":2,"percentComplete":0.0,"totalCount":0,"currentCount":0,"completed":false,"cancelled":false}
2017-0328 14:44:15 GMT 748.831513 Collab Log *416932 1d2af19e27c662447bcfeebd882d5c05 CURL DONE [UploadSignedURLsRequest] [] [299] 3.171815s {"method":"PUT","responseHeaders":[],"uri":"https://collab.cloud.unity3d.com/api/projects/9c8799cb-8410-4625-a345-4128a4ecf2da/uploads/5b4cf688-99b8-4684-8c66-7decc2892bfc"} Error: Analytics: UploadSignedURLs skipped because it was sent more than once in 0.10 seconds

2017-0328 14:44:15 GMT 748.873241 Collab Error 450820 1d2af19e27c662447bcfeebd882d5c05 CURL ERROR [UploadSignedURLsRequest] [Sorry, something went wrong, please try again later] [299] 3.213547s [Collab 2017-0328 14:44:15 GMT][Info] 'Sorry, something went wrong, please try again later' (56) returned in 'C:\Development\Unity_Staging\Editor/Src/Collab/Requests/UploadRequests.cpp' at line 104
[Collab 2017-0328 14:44:15 GMT] SubmitRequest failed, Reason: 299 Url: https://collab.cloud.unity3d.com/api/projects/9c8799cb-8410-4625-a345-4128a4ecf2da/uploads/5b4cf688-99b8-4684-8c66-7decc2892bfc Result:

2017-0328 14:44:15 GMT 749.508764 Collab Error *416932 5104524a45ac10242932ca9dc172ee0c JOB ERROR [CollabPublishAsyncJob] [Sorry, something went wrong, please try again later] [FAILED] 6.752542s {"comment":"","revisionId":"","running":false,"waitingForCompletion":true,"progressType":2,"percentComplete":0.0,"totalCount":0,"currentCount":0,"completed":false,"cancelled":true} [Collab 2017-0328 14:44:15 GMT][Info] 'Operation was cancelled' (22) returned in 'C:\Development\Unity_Staging\Editor/Src/Collab/Jobs/CollabPublishAsyncJob.cpp' at line 361

2017-0328 14:44:15 GMT 749.509073 Collab Log *416932 5104524a45ac10242932ca9dc172ee0c JOB COMPLETE [CollabPublishAsyncJob] [Sorry, something went wrong, please try again later] [FAILED] 6.752873s {"comment":"","revisionId":"","running":false,"waitingForCompletion":true,"progressType":2,"percentComplete":0.0,"totalCount":0,"currentCount":0,"completed":true,"cancelled":true} UPID Received '9c8799cb-8410-4625-a345-4128a4ecf2da'.