Interestingly just ran into the same problem with Army of the Dead X. 11 souls dropped and earned a plat armor gift, click through mission like normal, go to collect gift and nothing there. Check my soul count and says 2 souls to go until plat armor. Not sure what my count was before but has to be the same, since it told me I just earned an armor but need only two more to earn one. Only got on for one run before bed anyway, will see what it's like in the morning.