I made a modpack using MyServerIsCompatible and some other mods
But it crashes when starting up.
I went over to SuperMartijns642's discord server to get support since the problem inculded some of the mods they made.
They said i needed to go here since tehy don't know why your mod conflicts with theirs.
The logs and the modpack are added below.

latest.log
Modpack 1.zip

Using that mod seems to work. Thanks for the help!

Some additional info:
On Minecraft 1.12, both My Server Is Compatible and my core library work fine independently, but cause a crash when combined.

The crash seems to be caused by a mixin error from my core library. However, I don't see how this is only the case when My Server Is Compatible is installed.
Both mods only have one mixin into different classes (ForgeHooksClient and FMLClientHandler), so, as far as I know, those shouldn't conflict.
The mixin from my core library can be found here: https://github.com/SuperMartijn642/SuperMartijn642sCoreLib/blob/1.12/src/main/java/com/supermartijn642/core/mixin/LevelRendererMixin.java

Seems like that the mixin versions included in both mods are conflicting? I don't know why, because they seem to have the same version.
Adding this mod to your modpack should fix the issue -> https://www.curseforge.com/minecraft/mc-mods/mixin-0-7-0-8-compatibility