Most of my gnomes just stand around now, even when there's work to be done.
I'm encountering this as well... I noticed that it tends to occur most often when they're in a squad - I disband their squad and suddenly everyone springs into action. Put them back into a squad, and they go back to idling on stockpiles, beds, and other random spots.
Not sure if it's relevant, but the squad/formation I've been seeing them have trouble with is my "Gnome-Fu" (no armor, no weapon, Way of the Gnome) backup guards which all my gnomes who aren't in a dedicated/training squad are in. The training squads appear
to function properly when they're "off" their training shifts.
EDIT: The last sentence is incorrect. At 0600, when a new shift of guards should have gone on duty, the prior shift continued to sit in the Training room idling despite having jobs to do (and one wouldn't even go get a drink, despite being "Thirsty").
So I think this confirms it's somehow related to Gnomes being assigned to military roles. The fix beyond that? I haven't the foggiest idea - aside from just getting rid of your military for the time being, which is far from an ideal solution lol.