You could have a small flow starting.
Where is the nectar at? Is it near the brood or is it in the supers?
If it is in the supers, they may have run out of flow before it was capped. If it is around the brood, that is honey they are using to feed the brood.
Lift up the back of the hive to feel how heavy they are. I put the front edge of the hive box lined up on the front edge of the stand and leave an inch hanging over the back edge of the stand. This gives me a fingertip area to lift the hive and see how much it weighs.
If you lift your hive on a regular basis, when it is just starting, after inspections and after adding empty supers, you will bee able to judge if they are adding or loosing weight.
Jim Altmiller