Reproduction steps:
1. Open the attached “BitReaderWriter“ project
2. Open Test Runner (Window > General > Test Runner)
3. Run all tests

Expected result: Tests pass
Actual result: Tests fail

Reproduced with: 1.0.0 (2020.3.37f1, 2021.3.6f1, 2022.1.9f1, 2022.2.0b1, 2023.1.0a3)

Note: In the constructor, the m_BufferPointer variable is set to be the buffer plus the position, but then the position is added again in the WritePartialValue function

Code in WritePartialValue function:
byte* ptr = ((byte*)&value) + offsetBytes;
byte* bufferPointer = m_BufferPointer + m_Position;
UnsafeUtility.MemCpy(bufferPointer, ptr, bytesToWrite);

Suggested fix:
byte* ptr = ((byte*)&value) + offsetBytes;
UnsafeUtility.MemCpy(m_BufferPointer, ptr, bytesToWrite);