The cups on your putting green have sunk or gone uneven. Here is why, and the reset.

A cup sits in a cored socket at a set depth below the surface sand. Sand migrates downhill and toward low points with every rain the same way infill does on any turf lawn, and a fixed object like a cup collar, a ring, or a flagstick sleeve creates exactly that kind of low point, so sand collects unevenly around it, a hump on one side, a bare rim on the other, or extra sand built up around the collar that makes the cup look like it has sunk even when it has not moved. Separately, a cup socket set into ground that has not fully settled since the green was built, or one sitting over a soft spot in the base, can genuinely sink over a season or two, more common in the first year or two after a new green.

Lay a straightedge or a flat board across the cup and the green around it. If the collar sits noticeably below the board with the rest of the green reading even, uneven sand distribution is the likely cause, and checking the depth on each side of the cup usually confirms more sand on one side than the other. Lift the cup collar, most are designed to come out, and check the socket underneath for standing water or a soft, give-way feel; a socket that is genuinely settling feels loose or noticeably softer than the base elsewhere on the green.

Lift the cup, check and firm the base under and around the socket, reset it level, then top-dress and brush sand back in evenly to match the depth of the rest of the green, checking with the straightedge as you go. This is routine work within a putting green restoration visit and, on a green under regular care, is usually caught before a player would notice it mid-putt. A socket that keeps settling in the same spot after a proper reset points to a base issue right at that location, which needs the ground below it compacted, occasionally a small excavation and rebuild at that one cup, still far short of rebuilding the whole green.

Work more than one cup location into the green where space allows, and move which one is in play occasionally, the way a golf course rotates cups, so sand and wear do not concentrate around a single socket for years. A quick straightedge check each spring, right after top-dressing, catches drift before anyone notices it. Keeping the whole green top-dressed on schedule is what keeps the cups from becoming the one spot that collects all the wandering sand.