Beginning with the Paris Exposition of 1878, the instrument's popularity rebounded. The Exposition was one of many stops for a popular new performing group the Estudiantes Españoles (Spanish Students). They danced and played guitars, violins and the bandurria, which became confused with the mandolin. Along with the energy and awareness created by the day's hit sensation, a wave of Italian mandolinists travelled Europe in the 1880s and 1890s and in the United States by the mid-1880s, playing and teaching their instrument. The instrument's popularity continued to increase during the 1890s and mandolin popularity was at its height in "early years of the 20th century." Thousands were taking up the instrument as a pastime, and it became an instrument of society, taken up by young men and women. Mandolin orchestras were formed worldwide, incorporating not only the mandolin family of instruments, but also guitars, double basses and zithers.

Answer this question, if possible (if impossible, reply "unanswerable"):  When did the mandolin's poplarity not rebound?
unanswerable