Sir Alexander Armstrong, 6th Lord of Mangerton - Two fathers, David is the wrong one.

5th Laird-- Thomas Armstrong - 15th century. 1. Alexander Armstrong (6th Laird) 2. John Armstrong of Whithaugh 3. Will Armstrong of Chingils 4. George Armstrong of Ailmure

According to the source provided in his bio, his father was Thomas Armstrong, 5th Laird of Mangerton. David appeared after a recent bad merge, here:

https://www.geni.com/merge/view?revision_id=78733793310

Another discussion was started in 2015 with regard to numerous issues with the Armstrong genealogy, but received no response, apparently. https://www.geni.com/discussions/151005?msg=1051464