1. It may be that the capacity of your rice cooker is not big enough, the porridge is added too much, there is no space to hold the steam, so it overflows.

2. It is also possible that you cook too long, the porridge cooks too long, and the soup in the porridge evaporates too much, so it overflows.

3. It is also possible that you didn't put the lid on the pot, which caused the heat not to be suppressed and the steam overflowed.