Here is the screen shot, and the dragon stone is not showing up in the inventory after the quest. Also the dragon squad mission is not found in my quest log as well.
Sure, but your screen shot isn't even this server so you should prob report to your game's server so the staff can look into it.
Based off the tags I'm assuming this is official GMS reboot? Scrolling was removed from reboot, and the dragon stone counts as a scroll so you're unable to get it. Not a bug, but also very much not the right place for reboot/gms issues