When loading an instance of this mod and another mod (that is missing one of its coremods), normally forge would have a screen that tells the user what mods are missing. But right before this screen appears, the game freezes in this screen (below), which i originally thought was a forge issue, until i tracked this mod down, the hard way.

here is the original forge issue post:
MinecraftForge/MinecraftForge#6317

here is the forge forum post that I made after they rejected my issue for support instead:
https://www.minecraftforge.net/forum/topic/77928-1122-freezeing-on-loading-unleashedresources-during-phase-1-of-loadup/

logs:
debug.log
latest.log

I'm surprised that you haven't thought of the possibility that forge could have a missing coremods screen, it occurs quite often especially with pack makers... really annoying when you don't know what the mod is...

That's not only custom loading screen - what mod adds the "ping" game?

(or have you tested with only CLS and a mod that is missing a coremod?)