(Assuming you’re trying to use an existing project.)
This is a known issue. There’s an incompatibility issue between C11/C12 and C13 mix consoles. You’ll need to open the project in C12 open all the mixers, open all the racks, save the project then open it in C13. It’s a pain in the derriere.
See my thread here, but there are others.
NOTE, it only affects projects saved in C11/12. Older versions (C10 etc) or new projects created in C13 work as expected.