As per my understanding during his lifetime, Gautama Buddha, had attained Nibbana with residue. And after death he attained Parinibbana (or Nibbana with no residue).
Nibbana with residue is defined as following :
What, bhikkhus, is the Nibbana-element with residue left? Here a bhikkhu is an arahant, one whose taints are destroyed, the holy life fulfilled, who has done what had to be done, laid down the burden, attained the goal, destroyed the fetters of being, completely released through final knowledge. However, his five sense faculties remain unimpaired, by which he still experiences what is agreeable and disagreeable and feels pleasure and pain. It is the extinction of attachment, hate, and delusion in him that is called the Nibbana-element with residue left.
During his last days Gautama Buddha felt sharp pain and illness which he suppressed. In other words Gautama Buddha suffered because he was yet to reach his final Nibbana (Nibbana with no residue).
And soon after the Blessed One had eaten the meal provided by Cunda the metalworker, a dire sickness fell upon him, even dysentery, and he suffered sharp and deadly pains. But the Blessed One endured them mindfully, clearly comprehending and unperturbed.
We describe all sufferings using dependent co-arising.But dependent co-arising of suffering of Gautama Buddha is only possible if Gautama Buddha had failed to achieve the complete cessation of ignorance. Because if he had completely destroyed the ignorance at the very beginning then suffering would have ceased automatically.
From the remainderless fading & cessation of that very ignorance comes the cessation of fabrications. From the cessation of fabrications comes the cessation of consciousness. From the cessation of consciousness comes the cessation of name-&-form. From the cessation of name-&-form comes the cessation of the six sense media. From the cessation of the six sense media comes the cessation of contact. From the cessation of contact comes the cessation of feeling. From the cessation of feeling comes the cessation of craving. From the cessation of craving comes the cessation of clinging/sustenance. From the cessation of clinging/sustenance comes the cessation of becoming. From the cessation of becoming comes the cessation of birth. From the cessation of birth, then aging & death, sorrow, lamentation, pain, distress, & despair all cease. Such is the cessation of this entire mass of stress & suffering
My question is: How did the suffering of Gautama Buddha(no matter how small) arise or co-arise?
My guess is that with incomplete cessation of ignorance came incomplete cessation of fabrications. From incomplete cessation of fabrications came incomplete cessation of consciousness. From incomplete cessation of consciousness came incomplete cessation of name-form. From incomplete cessation of name-form came incomplete cessation of six sense media. From incomplete cessation of six sense media came incomplete cessation of contact. From incomplete cessation of contact came incomplete cessation of feeling. From incomplete cessation of feeling came incomplete craving. From incomplete cessation of craving came incomplete cessation of clinging/sustenance. From incomplete cessation of clinging/sustenance came incomplete cessation of becoming. From incomplete cessation of becoming came incomplete cessation of birth. From incomplete cessation of birth came incomplete cessation of aging ,death ,sorrow,pain , distress.
I am not saying that Buddha was ignorant but that there is a possibility that there are levels of ignorance which one needs to transcend like the levels of jhanas.