I think Ame and Fauna are leaving because of a shared manager stifling them and making them feel constrained because of their brand image bullshit and the timeline matches. Fauna's last stream where she attached something to her Live2D model was her Deltarune stream November of last year, after that she only attached things to her 3D model which has access to a free library of 3D assets for use. Ame's last stream where she attached a PNG to her Live2D stream was her Refind stream, but before that was her Mario Wonder streams which she dropped and went AWOL for several weeks. I think Ame was told after the Wonder streams that she couldn't alter her Live2D model with assets to resemble the game and this upset her and she went AWOL in protest, after which she did the Refind stream with Christmas assets for which she got told to stop doing it entirely. This also matches up with Ame not being able to use her alternate 3D models and Fauna not being allowed to use her low poly3D or Anuaf palette over "brand image" either.

Now imagine if you were in their place and was being constrained over this bullshit while watching Advent and Kiara get away with the same shit regularly. Wouldn't you be pissed off?