Did you change the censor type to BLUR or PIXELATE? If left on BLACK, a black square will appear. 
If more blurriness is needed, use a mask with the BLUR effect instead of Censor.
If you take a minute to share your project, someone here will come up with an answer. The process is easy, quick and can be private. Follow these steps carefully...
Back up --- With your project on the timeline, click on MENU at the top-left. Click FILE|BACK UP PROJECT FILES TO FOLDER. Choose a folder and SELECT FOLDER.
Upload --- Use a free server - Google Drive, MS OneDrive, etc.* - to upload the saved, numbered FOLDER. Do NOT upload the individual VPJ or export file.
Get link --- Get a public link. If using Google Drive click GET SHAREABLE LINK. Change "restricted" to "anyone with the link can view" Click COPY LINK | DONE.
Share --- Paste that link here, or click the folder at the top-right of this forum to message it privately to me. It won't be shared.
* Before uploading, right-click the folder, click PROPERTIES. Look at the File Size to confirm that it's not too big for the free space on the server.