Csharp 当前代码Cosmos DB 3.37.1：PartitionKey key key mismatch exception

这个问题已经被问了很多次，甚至有几次答对了，我都看过了，然而，无论我做什么，它都会发生在我身上.以下是代码:

正在创建容器:

string partitionKeyPath = $"/{_userId}";
_container = await database.CreateContainerIfNotExistsAsync(_containerName, partitionKeyPath);

然后，当添加我的聊天对象的时候:

if (_container != null)
{
    Chat? chat;
    bool newChatCreated = false;
    try
    {
        // Attempt to read the Chat item. If it exists, add the ChatItem to it.
        chat = await _container.ReadItemAsync<Chat>(chatId, new PartitionKey(_userId)).ConfigureAwait(false);
    }
    catch (CosmosException ex) when (ex.StatusCode == System.Net.HttpStatusCode.NotFound)
    {
        // If the Chat item does not exist, create a new one.
        chat = new Chat
        {
            id = chatId,
            _userId = _userId,
            ChatItems = new List<ChatItem>(),
            ChatName = chatName,
            IndexName = indexName,
            TimeCreated = DateTime.Now.ToString("yyyy/MM/dd-HH:mm:ss.fff")
        };

        ContainerProperties props = await _container.ReadContainerAsync();
        _logger.LogInformation($"PartitionKeyPath: {props.PartitionKeyPath}");

// Exception happens on the next line in CreateItemAsync !!!
        await _container.CreateItemAsync<Chat>(chat, new PartitionKey(_userId));

        newChatCreated = true;
    }

    chat?.ChatItems?.Add(chatItem);

    if (newChatCreated)
    {
        // Update the Chat item in the database
        await _container.ReplaceItemAsync<Chat>(chat, chatId, new PartitionKey(_userId));
    }
    else
    {
        var patchOperations = new List<PatchOperation>
        {
            PatchOperation.Add("/ChatItems/-", chatItem)
        };
        await _container.PatchItemAsync<Chat>(chatId, new PartitionKey(_userId), patchOperations);
    }
}
else
{
    _logger.LogError("_container is null");
    return false;
}

用作PartitionKey的_UserID全部是字母数字小写:"supportgpt4office ecom". PartionKeyPath相同，但前缀为‘/’，即:"/supportgpt4office ecom"(通过在调用之前记录它来验证).

有谁能给我解释一下这是怎么回事吗？ 顺便说一句，我正在运行最新的CosmosDB版本: Microsoft.Azure.CosmosDB 3.37.1