Cracked mystery snail shell

[Liambomb123]

Big crack down half his shell

 

[Liambomb123]

I want to know what probably caused this and how i can fix it he is in a tank with other mystery snails and guppies just moved him from one tank to another but all my tanks are same ph same temp and all that good stuff i move most of my snails around to clean tanks just getting a colony going now so wont have to do that anymore but need help with this little guy since he is my biggest and is gonna become a mum or dad since i found a clutch

 

[Liambomb123]

Here is some photos