Unknown Sender, is it on the blockchain?

What does “Unknown sender” mean in an internal transaction? If the transaction hash is available, doesn’t that mean I can get the sender’s address?

Because this is a manual transaction, I do not think the system is programmed to look at the hash at all, the hash in this case is just a side note for the user.
If this was an API transfer, then it would populate with the address it was sent with.