90% sure you just was zoomed out too far, when you are zoomed out far you can't issue a reclaim order.
It used not to be a problem cause people would always zoom in to reclaim, mostly because it would not even render when you zoom out
But now FAF increased visibility of reclaim and you can see it without zooming in
AND people got bigger monitors and greater screen resolutions and it is easyer to click reclaim while zoomed out
For now only thing you can do is to zoom in and make sure your orders snap to the reclaimables, like when you click in the corner of the rock or tree group, order should snap to the middle of the rock or to the middle of the tree group...
Edit: you also can use right click to click reclaim, when you hover over reclaim cursor will change to reclaim icon letting you know you can issue a reclaim command with a right click, but when you are zoomed out to far and hover over reclaim cursor will not show reclaim icon
FAF should probably add a config to set the height at witch you can't make reclaim orders.
Not being able to set reclaim orders when zoomed out is sometimes very usefull when you want to micro ACU and try to avoid clicking on the trees or wrecks