How are keys for lightning channels currently created? Keys for creating lightning channels seem to be derived differently than in usual bitcoin wallets. Lightning node data corruption, despite backup of master seed phrase, seems to prevent recovery of channel keys. How are channel keys currently derived, and why is recovering these keys with a corrupted node extremely difficult? 

This question is in response to #3 of the following video (timestamped) https://www.youtube.com/watch?v=5fMv8MpzLgQ&amp;feature=youtu.be&amp;t=143
While I have experienced the same situation as the person described in the video the information is only partially true. 

It is very well described in BOLT 03 how keys are being derived. The general derivation of the keys you are looking fore is described in this formula:


  privkey = basepoint_secret + SHA256(per_commitment_point || basepoint)


so what you can see is that your secret is added with a per_commitment_point which contains information about the channel state. This is done to increase your privacy and is the reason why lightning nodes need the channel state in order to derive the keys from your seed.