project-system: Restore stuck & can't build due to missing ProjectRestoreInfo

Since we converted our project (Xenko) to new project system, we often (esp. after switching branches) end up in a broken state.

When trying to build, we end up with something like this in the log:

Error occurred while restoring NuGet packages: System.InvalidOperationException: The operation failed as details for project SiliconStudio.Core.Design.Tests could not be loaded.
   at NuGet.PackageManagement.VisualStudio.NetCorePackageReferenceProject.GetPackageSpecsAsync(DependencyGraphCacheContext context)
   at NuGet.PackageManagement.DependencyGraphRestoreUtility.<GetSolutionRestoreSpec>d__7.MoveNext()

Build is totally stuck, i.e it stays like this:

1>FastUpToDate: Project information is older than current project version, skipping check. (SiliconStudio.Core)
Error occurred while restoring NuGet packages: The operation failed as details for project SiliconStudio.Core.Design.Tests could not be loaded.
2>FastUpToDate: Project information is older than current project version, skipping check. (Irony)
3>FastUpToDate: Project information is older than current project version, skipping check. (SiliconStudio.ExecServer)

Restarting VS & git clean (.vs) usually doesn’t seem to fix the issue.

I can sometime (but not always) get out of the situation by: (1) Killing all MSBuild process (2) Doing a manual (command-line) nuget restore (maybe this is probably what helps fix it since VS doesn’t need to restore anymore) (3) Sometimes (random magic) git clean and/or VS restart might also be necessary (4) If this doesn’t work, I end up doing a new checkout (takes a while)

It happens quite easily on multiple separate PC and users, so not a local issue.

I investigated little bit and it seems NominateProject is not called on this specific project. Not sure if related, but here’s what I noticed when debugging project-system:

• Some NominateRestore calls (but only about 20 of them, out of 100+ projects)
• A big Microsoft.Build.Exceptions.BuildAbortedException exception

  Exception thrown: 'Microsoft.Build.Exceptions.BuildAbortedException' in Microsoft.Build.dll
  Build was canceled. A node of the required type InProc could not be created.
  

  Could this be the main issue?
• Hundreds of System.OperationCanceledException in Microsoft.VisualStudio.Threading.dll
• A few more NominateRestore (but only for projects that already ran through NominateRestore before).

Sorry for the lack of easy repro, it is quite a big project that we can’t share publicly yet. This happens often and quite hard to get out, so quite a big blocker & slowing us down quite a lot.