.Net: Bug: [InMemoryVectorStore] "Collection does not exist" when calling UpsertAsync after GetCollection

[P47K0]

Describe the bug
Calling UpsertAsync (or batch) on a collection obtained via GetCollection throws:

Call to vector store failed. Collection 'test' does not exist.

Even after:

• GetCollection succeeds
• Dummy upsert attempts (single record, non-zero vector, empty batch) fail with the same error

To Reproduce

var store = new InMemoryVectorStore();
var collection = store.GetCollection<string, MyRecord>("test");
var record = new MyRecord { Id = "dummy", Vector = new float[1024] /* non-zero values */ };
await collection.UpsertAsync(record);  // throws "Collection does not exist"

Expected behavior
UpsertAsync will insert the provided records

Screenshots
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Platform

• Language: C#
• .NET: 10.0
• Source:
  • Semantic Kernel version: 1.70.0
  • Connector: Microsoft.SemanticKernel.Connectors.InMemory 1.70.0-preview
• AI model: nomic-embed-text via ollama
• IDE: Visual Studio 2026 Pro
• OS: Winsows 11 x64
• GPU: Intel Arc iGPU

Additional context
You can see my simple Hangman game where I encountered the issue here:
https://github.com/P47K0/SKOrchestrationPractice