A part of the data models are missing in my single player world, when right clicking a mob (which is already not showing in JEI/REI, it says: no known models exist for this specimen

When looking at the log it also says: Failed parsing data models file hostile networks:phantom (and for all the other mobs not present)

Here are the data models that do get loaded:

Here is the log from starting my modpack, loading the sp world and right clicking a data model on the mob.

Log on mclo.gs

You are missing the entity key on your data model json file. Unfortunately the error is useless since it doesn't name the problem, so I can go update that.