TWIS shares registers and other resources with other peripherals that have the same ID as TWIS.
Therefore, you must disable all peripherals that have the same ID as the TWI slave before TWIS can be configured and used. Disabling a peripheral that has the same ID as the TWI slave will not reset any of the registers that are shared with TWIS. It is therefore important to configure all relevant registers explicitly to secure that TWIS operates correctly.
The Instantiation table in Peripherals shows which peripherals have the same ID as TWIS.