soft shallots (were being stored to plant out this aut)

If they've deteriorated that quickly they must have either lost too much water through being stored somewhere too hot, or, despite your efforts, are starting to rot.

The rot isn't always visible from the outside - cut one in half and see whether any of the flesh is soggy looking and/or mouldy (usually starts from the neck end.)

Obviously best to plant healthy bulbs - you might get away with slightly dehydrated ones but definitely won't get anywhere with rotting ones.