Every version of kicad did have the cache lib system (At least since 2013. I did not use any older version).
This special library contains a copy of every symbol that is used inside the schematic. (It is an insurance against deleting or changing a symbol in your source libraries.)
For details see my post above.
Massive problems must be expected if this special file is missing from a project. I suggest you make an issue on the github project and ask the owner to upload this file. (My guess is they do not know how important this file is.)
If it is known which library under what version was used to create the project then it is possible to get kicad to recreate the cache lib.
One would need to setup the library tables such that they agree with the projects expectations and open the schematic. I am not sure if the cache lib is created when opening, when closing or on save.
Special care must be taken if the project was created in v4 or earlier as the remap process relies on the cache lib as well. For details about that see: Converting KiCad version 4 projects to version 5 (Remap a project)