During the painting of the ceiling fessco, payments from Pope Julius II "the Warrior Pope" were strained and infrequent according to Michelangelo. This is due to the Pope leading the Papacy's erupting war in Bologna against French troops in 1510.

What had happened was, Pope Julius II had been underfunding a previous commission of his from Michelangelo, the unfinished Tomb of Julius II which was to be a mausoleum unlike any other, due to a previous war that started 1506 I believe, where Pope Julius formed an alliance with some other leaders against Venice. Michelangelo rebels during this time due to the lack of payments and flees Rome back to Florence. Julius II, furious, demands Michelangelo return to him and submit, which the artist does and is then forced to spend another 2 years of his life casting a life-sized bronze of Julius II. Tragically, this bronze will survive only a few years before being torn down by a mob and melted down to make a cannon.

Afterwards, Michelangelo is then assigned to paint a fresco over the cracked, leaky ceiling of the Sistine Chapel ceiling. He protests, "non mia arte", "That is not my art", insisting he was a sculptor, not a painter. Of course, he is compelled by Julius II and is forced to teach himself how to paint. Michelangelo would spend the next 4 years on the fresco (including the destroyed bronze, a total of six years away from the project he really wanted to work on, the Tomb of Julius II).

I don't know much of why any of this political conflict happens, but in the middle of the painting of the ceiling fresco in 1510, the Warrior Pope leads Papal troops again to liberate Bologna from French troops, who were his former allies against Venice only a few years prior. This is likely why payments became smaller and more infrequent; war is more pressing than art most would say, although Michelangelo certainly did not appreciate living under such conditions. Although Michelangelo had a list of greivances during that time, including his recently widowed mother-in-law "betraying" his family by successfully suing for her dowry back (which meant Michelangelo no longer had any claim to inherit from his recently deceased Uncle Francesco's estate), Bramante and Raphael supposedly manipulating the Pope into assigning Michelangelo to work on the ceiling fresco in the first place, and Michelangelo being a severe, joyless complainer in general, although arguably justifiably so given the circumstances.

Still, he would complete it, infrequent payments and all, and eventually go back to working on the Tomb of Julius II by 1512.