I have a controller action which must run some tasks that don’t need to be awaited to return a response which is why I’m firing-and-forgetting those functions. However these functions are deadlocking hence never completing.

public async Task<IActionResult> AddPlayerToQueue(AddPlayerToQueueRequest request)
{
    //...

    if (request.MatchPrivacy == MatchPrivacy.Public)
    {
        // If the queue is full and there is another one which is compatible ready, tell the game to start the match
        _ = EvaluateMatchStart(request.Player.UserId); // Fire-and-forget. Don't need to await this function because it's not relevant to the action's scope
    }

    return Ok();
}

private async Task EvaluateMatchStart(long userId)
{
    //...

    await gameService.SendStartMatchMessageAsync([readyQueue, opponent]).ConfigureAwait(false); // Deadlocks despite using ConfigureAwait(false)
}

This is the code of a typed HttpClient

public class GameService(HttpClient httpClient, IConfiguration configuration) : IDisposable
{
    public async Task SendStartMatchMessageAsync(Queue[] queues)
    {
        //...

        // Send message
        HttpResponseMessage res = await httpClient.PostAsJsonAsync($"uri", new
        {
            message = JsonSerializer.Serialize(new
            {
                Teams = msgQueues
            })
        }); // Deadlocks

        res.EnsureSuccessStatusCode();
    }

    public void Dispose() => httpClient?.Dispose();
}