Credit to Asperger_Plays on the discord channel for finding this.

The mineral salt singularity is a single word on the name of the singularity itself. The item is "Mineral Salt" while the singularity is "Mineralsalt Singularity".

Actually, I can probably rename it with crafttweaker can't I.... I'll have to try that

I'm well aware of this, but it's a deficiency in the custom singularity mod, I can't use singularity names with multiple words

..and that didn't work