When one picks up a lore scroll with the Erudite perk, they are granted a level immediately, but the progress towards their next level remains at the same percentage. Effectively, the experience bar does not move.
Tip : This perk is the reason for why you should always leave the Lore Scroll room until the very end of a floor in case you get the Erudite Perk. Getting Erudite after picking up a Lore Scroll on the same floor feels really bad