tub drain won't stay down

We have a Kohler tub installed with a Kohler drain about 3 years ago. The drain is operated by a lever on the side of the tub. And for a while now if you fill up the tub the drain will float open. It won't stay down. If you push it down it opens back up again.

What could be the explanation for this unclosable drain? (It worked fine for the first 2.5 years.)

A tub drain?

I would think hair
Lots and lots of hair

Gimme head with hair
Long beautiful hair
Shining, gleaming,
Streaming, flaxen, waxen

Give me down to there hair
Shoulder length or longer
Here baby, there mama
Everywhere daddy daddy

Hair, hair, hair, hair, hair, hair, hair
Flow it, show it
Long as God can grow it

Let me note that we have nobody with long hair in the house. The drain seems to drain properly and speedily at the moment (though we have had some mysterious periods of slow draining). It's certainly not clogged. If I pull out the assembly from the drain which includes the plug that is supposed to seal the drain and the arm that connects to the knob which closes the drain, that assembly is clean. No signs of hair (or anything else). Is there someplace else to look? I think it's draining too fast for hair clog removing chemicals to do anything.

I have to admit also that I'm confused about how the presence of hair would create the particular behavior I've observed: The tub drains just fine, but if I try to close the drain it tends to float open in the tub water. It is possible to keep the water from draining out by holding the drain shut, but as soon as you let go it floats up and water starts draining out.

I realized I said the drain is operated by a lever but that's wrong. It's operated by a knob that you turn.

drain

Either a misadjusted operating rod, or misaligned drain plug when you insert it.

If I press the drain plug down it seals. Could it still be misaligned?

Where would I look for adjustments to the operating rod? (I didn't realize there was anything to adjust.)

Well, maybe rule out hair then.

Darn, I kinda like that song.

Some pop up drains can be lifted out and adjusted.

If it's a "Toe-Touch" plug, it might have become unthreaded from the drain. They can be tricky to reset.

I took a close look at the assembly over the weekend and noticed that there was indeed an adjustment for the height of the drain plug. I lowered it and the problem is solved.