uwp app bundle creation failed catastrophic error

Question

I am having following problem after I removed "creators fall update sdk preview" from target version of my project and I targeted my project to creators update SDK, while min version remains to anniversary update. I had to do it because on developer store, when I uploaded my created packages, they gave me error that some Mir.px something file is unsupported version, i.e : 16190 ( creators fal update sdk). So I tried to re target my project to creators update and then again created the packages and had the following errors.

Also note that I removed Threading.Tasks.Extensions package from my project to remove these warnings, ( because I wasn't using it anyway ) but these warnings still didn't go away.

update

tried to update the UniversalWindowsPlatform Package and got following error

Failed to download package 'Microsoft.Net.Native.SharedLibrary-x64.1.6.1' from 'https://api.nuget.org/v3-flatcontainer/microsoft.net.native.sharedlibrary-x64/1.6.1/microsoft.net.native.sharedlibrary-x64.1.6.1.nupkg'. The HTTP request to 'GET https://api.nuget.org/v3-flatcontainer/microsoft.net.native.sharedlibrary-x64/1.6.1/microsoft.net.native.sharedlibrary-x64.1.6.1.nupkg' has timed out after 100000ms. GET https://api.nuget.org/v3-flatcontainer/microsoft.net.native.sharedlibrary-x64/1.6.1/microsoft.net.native.sharedlibrary-x64.1.6.1.nupkg