Years ago I lived in a home that had a funky odor only in one closet. Maybe the attic insulation was poor above htis closet but the bad closet odor was do to a dead squirrel int he attic that was not even near the closet.

Take a look beyond your deck and make sure there is no other dead item . Although you are smelling the odor while on the deck it could be in another area in the yard.. Look in the gutters too and the down spouts

This is not a "deck"--not raised with space underneath...it is concrete patio with pavers added on top of the original concrete..
and we have been in the yard--there is nothing dead there...
We noticed the smell is more concentrated along the drain line cut into the concrete with a plastic slotted cover over it...

I poured some vinegar in the drain at different points and let it sit for while and then ran water from the hose through it...
That halped...also noticed that the people who laid the pavers did a poor job of getting the high point right so that both sides of the drain do just that--drain.
One side of the drain does carry water outside the screen cage into yard but the other side apparenlty doesn't drain at all--
ran quite a bit of water into it and nothing came out into that side of the yard...
My husband got some bleach today and we will try that tomorrow--so we can be sure all of the drain channel has gotten some...
I am thinking it is stagnant water which isn't evaporating since the slope for the drain is not done right...
and these people are worthless for fixing mistakes...
we had them out twice for other problem and they just can't get it right--
should never have hired them...
expensive mistake...

At our previous home the pool deck had a couple of the types of in-deck drain you are describing. What we found was that unless we kept the drain cleaned out (using a pressure cleaner) some sort of fungus would grow in one of them pretty much blocking any flow. It didn't have an odor exactly like you are describing but it did have a sort of stale, stagnant smell to it when it started to clog. Bleach and pressure cleaning seemed to take care of it.