New interportal.

and the monks disappeared. I tested it again after the game - the monks consistently disappear if you split the stack in an external garrison. Sometimes, if, for example, you camp with 5 units of horses, the griffins also disappear, and the horses become 3+1+1. It's a mystery.

Based on my observations, the weakest stack disappears. In your example, the griffins and monks are clearly weaker than 1 horse, so they disappeared during the battle (logically, if the battle is won, they should return; this needs to be tested). It remains to be assumed that if you had split the efreets into 3+3+3 and the horses into 3+2, the "pokemon" would have disappeared as well.