For non-power-of-two textures, mipmap construction gets more complicated. 
MORE COMPLICATED
Not impossible.
You god damned fucking retard. Kill yourself, I seriously hope you aren't one of the VRChat devs, because I'd kill all hope for a competent base game and just go find some third party client to buy to fix your shit. You know you fucked up when retarded russians can code a better client. For cheaper than VRC+ and 100million dollars in investor money.