I think I disagree here. While concentrating on the spell and you are asking it to find an object of a particular kind, it points you to the nearest example *at that time*. The spell says it points you to the nearest, and what constitutes the nearest can change over time.
Incidentally, I think you need to go with this interpretation because of other changes that could impact items during concentration. For example, let's say that I ask the spell to look for a round ball and it detects one 800 feet away. I continue to concentrate on the spell and start walking towards it. You, being the person you are, pop the ball and it deflates. At that time, it is no longer a round ball. If you think that the spell should detect the "original" target regardless of whether you change distance, you'd also argue I should still detect that deflated ball even if it is not a round ball anymore... but what if I toss it in a Sphere of Annihilation?
Also, asking it to find strawberries or a bunch of strawberries appears to be illegal. You can have it search for *a* strawberry, or *a* basket containing strawberries, but you must look for a singular object. Minor point, but it clears up other ambiguities (what is a bunch?).
Regardless, if you ask it to find a strawberry and the nearest one is 50 feet, but there is another one 60 feet away from you in the opposite direction, once you walk more than 5 feet towards the further strawberry it becomes the closest strawberry and you "switch" to detecting that strawberry.