% Causes exc_bad_instruction error in Swift

I have an app that generates a number of random CGPoints. When running on a device, everything seems fine. When running on the iPad2 simulator, I suddenly get the following error: (EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0))

When debugging this, I confirmed that rndValueY was NOT 0 - (it was 768), and that Int(arc4random()) evaluates to some large number as well - no 0 values. So why is this happening? And why only on simulator? Would love any input!