as mr irwin suggests those components are a possibility but i would only check those as a last resort because the orbital valve does not commonly give problems. But as BLey suggested the wheel sensors can also cause the wheels to act up if they are not adjusted correctly or are bad and not working. And i wouldn't trust the indicator light on them either, i have had the light work and the sensor still not work properly so doing a physical check with an ohm meter on the circuit would be the best course of action imo.
I've dealt with this before myself and would be my first action to check.
If these position sensors are not adjusted correctly or are bad they can cause the wheels to not lock in and can make them cycle incorrectly when changing steering modes on their own seemingly. When you change steering modes also make sure they are turning completely from lock to lock, a bad steering mode cylinder can allow the wheel(s) to drift out of position coming off the sensor and keep them from operating properly.