Speculation: The new birthday suits on DMM are breaking the girls' eye mods.

[fate1234]

The new birthday suits come with built-in colored contact lens functionality. It's possible that KT has modified the girls' eye models. Simply modifying the hash values is no longer sufficient to fix the mods. I once sought help from active mod creators on the forum, but they were all busy with their own work. Now Monica is also experiencing issues, which confirms my suspicion. The order in which the girls' eye color mods failed: Nyotengu, Kokoro, Tina, Koharu, Monica. I suspect Yukino will be next.

[fate1234]

我现在不怕新生日服来临了，我自己钻研出来解决办法了，唉，求人不如求己。女天狗眼睛颜色mod修复成功。

[knight77]

Probably same with the "oil" thing they added for the birthday suits. It changed the face texture when you apply it, so some of the skin mods didnt work anymore either.
Girls with the new birthday thingy probably got a new eye texture and you need a new mod to work again.

[fate1234]

4 hours ago, knight77 said:

Probably same with the "oil" thing they added for the birthday suits. It changed the face texture when you apply it, so some of the skin mods didnt work anymore either.
可能跟他们为裸体套装添加的“油”效果一样。涂抹后会改变脸部纹理，所以一些皮肤 mod 也失效了。
Girls with the new birthday thingy probably got a new eye texture and you need a new mod to work again.
拥有新生日特效的女孩可能换了新的眼睛纹理，需要安装新的 mod 才能再次使用。

The solution has long been provided in Makeup mod v2.3 created by avenger54 & Zzxiaoyi. Some characters do not have eye textures included in their original facial texture maps—Hitomi, for example. We can refer to Hitomi's Makeup mod to rewrite the .ini configuration files for other characters' Makeup mods, as well as use Photoshop to create new .dds texture files.This method is only applicable to the eye color changing sub-mod within the Makeup mod series. As for how to fix other mods that are affected by this issue, I haven't installed such mods before, so I haven't done any research on it.

Edited January 3 by fate1234