efcore: Must be reductible node

Describe what is not working as expected.

I am migrating to .NET 2.1, but it seems entity framework broke: This was working in 2.0:

var userId = GetUserId();
using (var ctx = _ContextFactory.CreateContext())
{
    return await ctx.UserStore
        .Where(us => us.ApplicationUserId == userId)
        .SelectMany(us => us.StoreData.Apps.Select(app => new ListAppsViewModel.ListAppViewModel()
        {
            IsOwner = us.Role == StoreRoles.Owner,
            StoreId = us.StoreDataId,
            StoreName = us.Role,
            AppName = app.Name,
            AppType = app.AppType,
            Id = app.Id
        }))
        .ToArrayAsync();

Now it throws

at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
   at BTCPayServer.Tests.UnitTest1.CanUsePoSApp() in C:\Sources\btcpayserver\BTCPayServer.Tests\UnitTest1.cs:line 1180
----- Inner Stack Trace -----
   at System.Linq.Expressions.Expression.ReduceAndCheck()
   at System.Linq.Expressions.Expression.ReduceExtensions()
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteExtensionExpression(Expression expr, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteMemberExpression(Expression expr, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.MemberAssignmentRewriter..ctor(MemberAssignment binding, StackSpiller spiller, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.BindingRewriter.Create(MemberBinding binding, StackSpiller spiller, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteMemberInitExpression(Expression expr, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpressionFreeTemps(Expression expression, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.Rewrite[T](Expression`1 lambda)
   at System.Linq.Expressions.Expression`1.Accept(StackSpiller spiller)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteLambdaExpression(Expression expr)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression expression)
   at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.AddArguments(IArgumentProvider expressions)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteMethodCallExpression(Expression expr, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpressionFreeTemps(Expression expression, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.Rewrite[T](Expression`1 lambda)
   at System.Linq.Expressions.Expression`1.Accept(StackSpiller spiller)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteLambdaExpression(Expression expr)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression expression)
   at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.AddArguments(IArgumentProvider expressions)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteMethodCallExpression(Expression expr, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression expression)
   at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.AddArguments(IArgumentProvider expressions)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteMethodCallExpression(Expression expr, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression expression)
   at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.AddArguments(IArgumentProvider expressions)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteMethodCallExpression(Expression expr, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpressionFreeTemps(Expression expression, Stack stack)
   at System.Linq.Expressions.Compiler.StackSpiller.Rewrite[T](Expression`1 lambda)
   at System.Linq.Expressions.Expression`1.Accept(StackSpiller spiller)
   at System.Linq.Expressions.Compiler.LambdaCompiler.Compile(LambdaExpression lambda)
   at System.Linq.Expressions.Expression`1.Compile(Boolean preferInterpretation)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.CreateExecutorLambda[TResults]()
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.CreateAsyncQueryExecutor[TResult](QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore[TFunc](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.ExecuteAsync[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1.System.Collections.Generic.IAsyncEnumerable<TResult>.GetEnumerator()
   at System.Collections.Generic.AsyncEnumerableHelpers.ToArrayWithLength[T](IAsyncEnumerable`1 source, CancellationToken cancellationToken)
   at System.Collections.Generic.AsyncEnumerableHelpers.ToArray[T](IAsyncEnumerable`1 source, CancellationToken cancellationToken)
   at BTCPayServer.Controllers.AppsController.GetAllApps() in C:\Sources\btcpayserver\BTCPayServer\Controllers\AppsController.cs:line 178
   at BTCPayServer.Controllers.AppsController.ListApps() in C:\Sources\btcpayserver\BTCPayServer\Controllers\AppsController.cs:line 44

Note that if I comment

            StoreId = us.StoreDataId,
            StoreName = us.Role,

it does not crash.

<PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="2.0.2" />
<PackageReference Include="Microsoft.AspNetCore.App" Version="2.1.0-rc1-final" />
<PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version=" 2.1.0-rc1-final" PrivateAssets="All" />

Workaround:

return await ctx.UserStore
    .Where(us => us.ApplicationUserId == userId)
    .Join(ctx.Apps, us => us.StoreDataId, app => app.StoreDataId,
    (us, app) =>
    new ListAppsViewModel.ListAppViewModel()
    {
        IsOwner = us.Role == StoreRoles.Owner,
        StoreId = us.StoreDataId,
        StoreName = us.StoreData.StoreName,
        AppName = app.Name,
        AppType = app.AppType,
        Id = app.Id
    })
    .ToArrayAsync();