With I2C any device on the bus can hold the line low. I would first try to determine whether it is the master or slave device that is holding SCL low after that first transition.
In the debugger after the error state has occurred, check the status register of the RIIC peripheral for any clues to abnormal state. Check the I2C Bus Control Register 1 (ICCR1) to see whether the RIIC line state matches what you see on the scope. Compare the line monitor bits to the output control bits. That will tell you if it is the RIIC or the touch screen that is holding the clock line low.
-Gerald