BinaryReader 返回正确的字符串，但缺少前三个字符

问：

我编写了这段代码来从文件中读取。当它从文件中读取时，它会返回正确的字符串，但它不会保存前三个字符。该程序旨在令人满意地处理游戏中的保存文件。

   using System.Diagnostics;
   using System.IO;
   using System.Security.Cryptography.X509Certificates;
   using System.Text;

   namespace SatisfactorySaveParser
   {
        public class FSaveHeader
        {
            public int SaveHeaderVersion;
            public int SaveVersion;
            public int BuildVersion;
            public string MapName;
            public string MapOptions;
            public string SessionName;
            public int PlayedSeconds;
            public long SaveTimeStamp;
            public byte SessionVisibility;
            public int UnrealEngineVersion;
            public string ModMetadata;
            public int ModFlags;
            public string SaveIdentifier;

            public void Parse(FileStream stream, string filename)
            {
                BinaryReader reader = new BinaryReader(stream, Encoding.UTF8);
                int Length = filename.Length;

                SaveHeaderVersion = reader.ReadInt32();
                SaveVersion = reader.ReadInt32();
                BuildVersion = reader.ReadInt32();
                MapName = reader.ReadString();
                MapOptions = reader.ReadString();
                SessionName = reader.ReadString();
                ModFlags = reader.ReadInt32();
                PlayedSeconds = reader.ReadInt32();
                SaveTimeStamp = reader.ReadInt32();
                SessionVisibility = reader.ReadByte();
                UnrealEngineVersion = reader.ReadInt32();
                ModMetadata = reader.ReadString();
                ModFlags = reader.ReadInt32();
                SaveIdentifier = reader.ReadString();
            }
        }
    }

我尝试了二进制读取器类的不同方法，以及从文件中读取的不同方法。