Could "Nobody is expecting his arrival" be accepted? I know that "čeká" can also be used when expecting a child...
Notice that expecting a child is "čekat dítě", not "čekat na dítě". "Čekat na dítě" would be "to wait for a/the child". So here it is really waiting, not expecting. Expecting would be "Jeho příjezd nikdo nečeká/neočekává.".
Nobody's waiting for his arrival??!! Why that is not correct?
If you could be a bit sparing with your question marks and exclamation marks it would look less rude and people might have more incentive to help you.
The contractions are handled centrally by Duolingo software. Perhaps it is doing a bad job here.
The forms with contractions tested "red," so Duo is apparently not playing nice here. I have manually added them.