The Avignon Papacy was the period from 1309 to 1376 during which seven successive popes resided in Avignon.
Would not the Avignon Papacy be considered a change in the Constant Duration of the Church, which expresses In lasting substantially unchanged for so many centuries?
No. The physical location of the Pope's residence is an accidental/nonessential quality of the Church. Furthermore, the change was not lasting as it ended with Pope Gregory XI who returned the See back to Rome. It was a brief disruption caused by political pressure.