Newbie question - desert attrition?

[PSeFKa]

Hello guys. I'm new here and to the mod but not to the game. I haven't met something like attrition in MTW2. I'm playing as Crusades States and in first turn I sieged Gaza and next turn I realised that I lost approximately half of my forces. That happened again while sieging Damascus and Cair. It doesn't happen with small army. Also once my general who was sieging Cair, after loosing half of the forces, retreated to fort without my order. I can't find any info about that feature, so I'm asking you if that's bug or something implemented and what are the requirements. I don't use Bym's Grim Reality. Also it's SS 6.4

[Dekhatres]

there's no attrition in med2, are you playing in hotseat mode ? because if yes then you probably forgot to turn off autoresolve