The documentation states: Returns the highest power of 2 in the differing lower bits of start and end. This means the function should identify the highest power of 2 in the bits where start and end differ.
The function does not return the highest power of 2 in the differing lower bits; rather, it uses the most significant differing bit to create a mask and apply it to (end - 1). 
https://github.com/code-423n4/2024-05-arbitrum-foundation/blob/6f861c85b281a29f04daacfe17a2099d7dad5f8f/src/challengeV2/libraries/EdgeChallengeManagerLib.sol#L574-L588
