The imam made a mistake and was required to perform the prostration for forgetfulness after the closing salam, and some of the followers had missed a rak'ah or more, so when the imam said the first salam

The questioner : O Shaykh, regarding the prostration for forgetfulness... this is the question, and this is a case that occurred: an imam made a mistake, and his prostration was required after the salam. Some of the followers had missed a rak'ah or two. When the imam said the first salam to prostrate after the salam, some of the followers stood up to complete what they owed. What is their situation? Do they return to prostrate with the imam, or do they prostrate after they have completed what they missed, or is following the imam dropped from them?

The Shaykh : They do not follow the imam.

The questioner : And they return, even if they had started the al-Fatihah?

The Shaykh : They return from their mistake.

The questioner : Even if they had started the al-Fatihah?

The Shaykh : Yes