Peace be upon you. According to Ayatollah Khamenei, washing the left hand for the third time invalidates the wudu, and the prayers performed with that wudu must be repeated, even if done out of ignorance. It is advisable to review question 2337 to understand the meaning of washing and when it becomes the second or third wash.
According to Ayatollah Sistani, it is a recommended practice in wudu to wash twice, and it is preferable not to wash the left hand twice to ensure the remaining moisture is used for wiping. The issue with washing three times is that it requires using new water, while the wiping must be done with the moisture left after the first or second wash, not after the third. If a person was ignorant and did not harm their wudu by washing three times, their wudu is considered valid, and thus their prayers and other acts dependent on the validity of wudu are also valid. However, if they were negligent in learning the rulings or harmed the validity of their actions, there is no way to correct their prayers and acts. Yet, if there is a fear of total rebellion, it is not advisable to order them to make up their worship, as Allah may bring about a change in their situation.
It is also recommended to review question 2337 for further clarification on the meaning of washing and when it becomes the second or third wash.
May you be successful in all good deeds.