حل خطای A second operation was started در Entity Framework

      System.InvalidOperationException: A second operation was started on this context instance before a previous operation completed. This is usually caused by different threads concurrently using the same instance of DbContext. For more information on how to avoid threading issues with DbContext, see https://go.microsoft.com/fwlink/?linkid=2097913.
    

      var station = dbContext.Stations.FirstOrDefaultAsync(t => t.Id == request.StationId && t.ShopId == request.ShopId);
....
await dbContext.StationTokens.AddAsync(accessToken);
await dbContext.SaveChangesAsync();