These were testing the GitHub - nbd-wtf/soma: a spacechain on signet with anyprevout, a spacechain toy implementation for transferring NFTs (the simplest example of blockchain I could come up with). These transactions correspond to blind merged-mining events (paid out of band with signet lightning) that would each yield a different spacechain block, as you can see they have an OP_RETURN with the hash of corresponding spacechain block.
The broken key path free spending part was a stupid vulnerability due to an overlooked detail. Please ignore, it was just a demo.