What earlier ideas and cultural practices were challenged during the 14th century?
There is no clear demarcation, other than purely chronological between the "long middle ages" and the Renaissance. many of the features that we characteristically associate with the Renaissance and Reformation in fact appeared in the fourteenth century.
The first was a theological and philosophical shift from the Platonism which dominated the 12th century to a fully fledged Aristotelianism, shifting from the high scholasticism of St. Thomas Aquinas to nominalism. This involved an increasing emphasis on study of the "liber mundi" or "the book of the world", i.e. science and natural phenomena as signs of the divine order. Some of this resulted in what we would now call science (such as optics, resulting in eyeglasses and telescopes) and some in alchemy and astrology.
The growth of nationalism in France and England involved attempts to wrest control of church temporalities and appointment of bishops from the Papacy to local control.
The Bible began to be translated into the vernacular, and various "heresies" arose which were precursors to the Protestant movements of the next centuries.