If you did not get a Level-Up like you thought you would, it means that the sum amount of XP you gathered over the past 10 weeks, after applying the depreciation system, was not enough for you to bump you to the next Artist Level. Please continue streaming to gather more Artist XP to reach the next milestone next week.
See also: Help Article: "What is the XP Fading system and how much of my XP fade per week?".