Dead bees in front of landing board

It seems I have had a late season swarm from both of my two hives.
Both have successfully requeened and I have new brood in both.  One of
my hives, though, has some strange things happening.  Might be nothing
but...

I am feeding with a bucket feeder set on top the inner cover and
inside an empty deep.  This week (getting colder) some of the bees
were grouped in a cluster in one corner of the deep - but above the
inner cover.  It was cold the night before but was not cold at the
time I entered.

The same hive had a whole bunch of rotten dead bees in the grass below
the landing board.  The other hive had none.

Any ideas - might be nothing - I'm a little paranoid as this is my
first winter with bees.

TIA,

Eric