Download issues on Windows 10

I have the latest version of Start.exe on a USB 3 flash drive.
I find that many apps will not download on my Win10 x64 Asus Z87 Haswell PC system. I have not seen any other issues with any other of my installed s/w on this system.
I have seen the behaviour change however from day to day.
My standard quick test (process) is to try downloading the A Note package using - Apps - Get More Apps - By Title - (click on Download column heading) - select 'A Note' - click 'Next' - It says 'connecting' and then I get an error box:
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PortableApps.com Platform
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Unable to download the file. This could be due to a proxy or network issue or the hosting server not permitting downloads from your location. File: http://downloads.sourceforge.net/portableapps/ANotePortable_4.2.4.paf.exe

Tests (all done using same adsl router in home):
1. The same process on the same Z87 system when booting from a Sergei Strelec WinPE 32-bit Win10 WinPE OS from the flash drive works.
2. The same process on the same Z87 system, but booting via Virtual Box to Sergei Strelec WinPE 32-bit OS from flash drive failed (although it worked yesterday!).
3. The same process on a different Win10 x64 notebook works OK (via WiFi)
4. The same process on the same Z87 system booting to Win8 x64 works OK
5. The same process on same Z87 system booting via Virtual Box to a freshly installed Win10 x64 1607 Build 14393 OS failed
6. The same process on same Z87 system booting via Virtual Box to a freshly installed Win7 failed

So it's looking like the network 'stack' on my Win10 PC is the problem.

However, the following packages DO download OK on my Z87 Win10 PC.
CCleaner
Geek uninstaller
Wise uninstaller
QDir
GPU-Z

BUT these packages do not ('fail to connect')...
Unable to download the file. This could be due to a proxy or network issue or the hosting server not permitting downloads from your location. File: http://downloads.sourceforge.net/portableapps/Pencil2DPortable_0.6.0.paf...
Unable to download the file. This could be due to a proxy or network issue or the hosting server not permitting downloads from your location. File: http://downloads.sourceforge.net/portableapps/SuperTuxPortable_0.5.1_Eng...
Unable to download the file. This could be due to a proxy or network issue or the hosting server not permitting downloads from your location. File: http://downloads.sourceforge.net/portableapps/TransmissionPortable_2.92....
Unable to download the file. This could be due to a proxy or network issue or the hosting server not permitting downloads from your location. File: http://downloads.sourceforge.net/portableapps/YUMI-UEFIPortable_0.0.0.6_...

Any ideas?

P.S. If I use 'direct connection' setting, then A Note, SuperTux, TransmissionPortable now download and install. Pencil2D and YUMI_UEFI still do not connect.