Glass shadows are broken

It's hard to explain the issue, but essentially, I'm using Chocapic13_V9_Extreme shaders, and specifically the way that those shaders handle glass transparency and how they cast shadow appears broken with Iris. I checked to make sure it's not an issue with the shaderpack or my settings, by using it alongside optifine and testing default settings alongside my preferred settings and tweaking them for a few hours. The option that should fix it is called "Stochastic_Transparent_Shadows" but it changes nothing for me. I'm on Iris version iris-mc1.20-1.6.4 The two images attached are how the exact same shaders with the exact same settings act on Iris compared to optifine. This issue makes using glass in my builds essentially impossible, I cannot get interior screenshots with my shaders, I cannot use stained glass to texture or color walls, I can't use glass panes on diagonal builds to smooth them (without casting nasty dark shadows), and they have a gross reflective texture while in shadow. I dont know how much of this is an issue between the shaders themselves and Iris, but everything works as intended on optifine, which is what frustrates me, and I need fabric + iris to make videos, cinematics, etc. for my builds