it appears to freeze on any call to twi.c that has a wait for TWI to become ready.
I assume that you when you are having problems you are making your RTC connections to the I2C pins on the LCD shield. I would investigate the connections between the Arduino and the shield and make sure that there is continuity.
Oh and RTC is Tiny RTC I2c module if that helps at all. Could not find a schematic on.
You can find a link to a schematic here: --> Real Time Clock Module | Hobbyist.co.nz
Don