The older light blue translucent stuff bay rails are prone to developing cracks which appear on the inside of the rails.
If your bike is still under warranty get them replaced by stating that they are a safety hazard when riding two up on the bike, the dealer will most likely replace them with the newer solid black rails.
If you do not have a warranty left you got the option of removing the rails, leaving the cracked ones on the bike or trying to get a company to make some cast iron ones.
Old cracked versions:
Newer black version:
A custom aluminum cast set from a company in South Africa: