Where in the United States are you?
Using sand to level a lawn may not be the best method and if too much sand is used to bring dips up that could smother the grass trying to grow there.
If that rotary mower is scalping the lawn the cutting height is set too low.

Central Texas with bermuda. Believe me when I say it; you can't smother this stuff. This spring I built a garden bed in the backyard and I've been fighting the grass pushing thru 1' of turkey mulch. I'm cutting it low because that encourages the bermuda to grow dense to choke the weeds out. It a deep green and thick where the lawn is level, but when a wheel hits a low spot it essentially scalps that grass.

1 inch of any mulch is not enough to suppress the growth of any "weed", or unwanted plant growth.
Even with Bermuda grass the proper way to level a depression is to cut the turf in a large X, peel back the sod, fill in the depression with good soil, and replace the sod.
Texas A & M does recommend cutting Bermuda grass about 1 inch high which means a rotary mower will have a tendency to scalp if the lawn is not quite level. The best mower for Bermuda is a reel type, not a rotary.