Is the person led in prayer considered to have been preceded by a pillar (of prayer) if the Imam is on his way to prostration while the person led in prayer is on his way to rising? And what is the ruling if the reason for being preceded is a whisper (from Satan) that leads to the person led in prayer delaying his bowing?

The cure for waswas (whispers/obsessive thoughts) is to ignore them and pay them no mind. Tranquility is achieved with the slightest stillness and is not negated by body movement as long as you are within the limits of bowing (ruku').

Standing erect from ruku' is a pillar (rukn) according to most scholars. If it is considered a pillar, then is falling behind the Imam in standing erect considered falling behind in a pillar or not? There are two views:

The first view: Falling behind in a pillar occurs if the Imam completes the pillar before the ma'mum (follower) begins it.

The second view: In addition to that, the Imam must be engaging in the subsequent pillar.

So, if the Imam precedes you by being on his way to prostration (sujud) while you are on your way to rising, this is not considered falling behind according to the view that stipulates the Imam's engagement in another pillar. However, according to the first view, it is considered falling behind.

Waswas is not an excuse for falling behind the Imam.

Therefore, one must begin rising from ruku' immediately when the Imam rises, and not delay due to waswas.