As a test, right click on the screen and see if you can make a zip file. if not your copy of win10 has gone bad, I have this problem right now.
If not something could be stuck in the upload queue you will need to do an offline-restart of the computer and fusion, then shut down and a restart of the computer then fusion, then when fusion is going turn the net back on, this should make the queue clear itself and upload what was stuck.
This has nothing to do with your problem just the computer.
Below is an error report this is one I forced the error is what is in red but the whole thing is needed, plus the model and the post you use so an apples to apples can be done, otherwise it is a guess.
Information: Configuration: Mach3 Turning
Information: Vendor: Artsoft
Information: Posting intermediate data to '/Users/daniellyall/Desktop/1001.nc'
Information: Total number of warnings: 1
Error: Failed to post process. See below for details.
...
Start time: Fri Dec 7 23:17:51 2018
Warning(/Users/daniellyall/Library/Application Support/Autodesk/Autodesk Fusion 360/XD8XKGFZX5G6/W.login/M/D20171116104230026/CAMPosts/mach3 turning.cps:680): octal literals and octal escape sequences are deprecated
Post processor engine: 4.2.1 42089
Configuration path: /Users/daniellyall/Library/Application Support/Autodesk/Autodesk Fusion 360/XD8XKGFZX5G6/W.login/M/D20171116104230026/CAMPosts/mach3 turning.cps
Include paths: /Users/daniellyall/Library/Application Support/Autodesk/Autodesk Fusion 360/XD8XKGFZX5G6/W.login/M/D20171116104230026/CAMPosts
Configuration modification date: Tue Dec 4 20:33:15 2018
Output path: /Users/daniellyall/Desktop/1001.nc
Checksum of intermediate NC data: e974bc8e2aa1c29f044a558696ebcbdd
Checksum of configuration: 93a4ab80a086449423d0b894263fdd4d
Vendor url: http://www.machsupport.com
Legal: Copyright (C) 2012-2018 by Autodesk, Inc.
Generated by: Fusion 360 CAM 2.0.5103
...
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Error: Milling toolpath is not supported by the post configuration.
Failed while processing onOpen().
###############################################################################
Error: Failed to invoke 'onOpen' in the post configuration.
Error:
Error: Failed to execute configuration.
Stop time: Fri Dec 7 23:17:51 2018
Post processing failed.