Both should be accepted. Càite a is an older spelling of càit a, the course currently uses both (they started with càite a, but use càit a in newly added sentences; both are accepted answers everywhere). It’s explained in the tips and notes.
That certainly should not be the case as the expected answer has an leabaidh – you either encountered some bug with generation of the tiles or you missed something (maybe you chose an instead of a for càite a bheil and you were left with only a or something like that?).