So, I have the Little Radiance custom knight skin as well as Child of Light and several other mods active, and grimmchild isn't spawning properly.
The skins are not the problem
If I quit and get back in, he's there, but as soon as I leave a room, he's gone, even if I go back to the previous room. The only exception I've seen so far is when I did TMG, he spawned perfectly well in the tent. Grimmkin still appear and are fightable though. I originally thought the problem was benchwarp, because he disappeared after a bench warp, but even leaving a room normally still makes him disappear.
This is not the case for weaverlings, they're working fine, as I had them equipped while I was experimenting
I've tried taking off the charm and putting it back on and he doesn't respawn, he only seems to respawn after I quit and relaunch.