Workbench can't see downloaded firmware
Sounds all such is expected behavior except unzip is failing 
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Just to provide you some clue about what you’re able to see Thanks Process Monitor.
1) You’re requesting for some firmware setup as identified not available already within firmware search path you can specify Thanks dedicated preferences.
2) Firmware process download is initiated within some temp directory created as child of first path of firmware search path. .xml file is basically download process trace.
3) Once download completed, a .zip file should be available. Such zip file is checked a bit (checksum ,...) prior moving next step
4) Expected behavior here if .zip is confirmed as fine is content extraction about
5) Back once extraction done some checks are performed to confirm data integrity
6) If all is ok temporary material is promoted to expected area (first path of firmware search path) and temporary repository removed.
7) Firmware setup process is then considered as finished. Firmware finder is invoked back. Finder should find obviously fresh installed firmware package ...
As within your current session step 4 is failing, step 7 finder process is failing to find within primary path expected firmware package (as not installed due to fail) and so is scanning back your full search path (which is including CubeMx tool default repositories ...)
Unfortunately I’ve no clue to explain why unzip process is failing on your side ... . I’ve no local issue and you’re first end user to complain about. I’m definitively convinced you’re facing some issue but which ?
Not an explanation about but workable work around should be to uncompress by yourself .zip file within an area part of search path. Having .zip & extracted material available within search path, firmware finder should be able to get your local firmware installation allowing you to go ahead ...
Feel free to comment / share back.
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