Units vanishing

I was playing as Germany and sent volunteers to spain, because I was playing historical. They land, and I order 2 tank units to attack an enemy tank unit. Both dissappear, instantly. There wasn't even a combat bubble, like you usually see. They just died suddenly.

I, of course, assumed I had just made a mistake and accidentally made them not have enough org, but didn't want to change it, so set up a cheat zo give me infinite. It still happen. I lost 18 units that way.

Can anyone tell me, what I did wrong?