Not a bug, it’s just how the game was designed.
The 10th node is a percentage of the hero’s base stats. Since Magni has a very low defense base stat, the gain for this node is actually less than the other fixed defense nodes.
Arguably not the best game design, especially for the increased emblem price node 10 costs, but not a bug either.
Thanks for that info cheers I understand now the shield that you put on dosnt count towards the percentage