This bug was fixed in Patch 1.97.42/1.73
I opened my restaurant and all employees arrived as expected. The Chef doesn’t want to enter the restaurant though. He stands outside and doesn’t move.
You can make the Chef enter the restaurant by resetting him.
Enter testingcheats true in the cheat console. Continue with the step 2.
If you don’t want your trophies on console to become invalid, use the cheat: resetsim <firstname><lastname>. Continue with step 4.
Hold Shift and click on your Sim at the same time.
Choose Reset Object (Debug)
After that the Sim should walk over to the stove and start cooking.
Some people have also reported that just interacting with the Chef helps but that didn’t work for me.