Just speculating, but something could have happened to miniature transformer driving EST tweeter. Sonion EST drivers come bundled with a separate transformer (used inside of all these IEMs). If your high frequencies are attenuated, the low end emphasis scales up.
Btw, per one of the previous comments about these EST drivers benefiting from more power, not higher voltage, but a source with a higher current drive (similar to Planars that benefit from higher current source). It's true, for example, I found M5 to scale up with Class A amplifiers or other DAPs with higher current drive (R2R2000 or N6ii w/E01). But it wasn't the case with EE Wraith, which could be related to its crossover design. Thus, not every IEM with EST driver will behave the same.