another picture of the outside corner cracking

a picture of the small cracks that are starting to appear on the inside.

"Could the cracking of the grout be from moisture from the opening of the concrete floor under the shower? i"

You pretty much hit it on the head there in that it is moisture related. For the most part, it could be from one of three things:

1) It could be moisture or moisture vapor coming though the unplugged hole, and wicking outwards to the curb. But if that was the case, in terms of there being significant moisture, you'd probably see signs of water presence or water damage at the base of the curb.

2) It could be the wood curb simply wicking moisture through the slab below.

The thing it, as best as I can read the photos, it appears that the majority of the swelling is on the top of your curb. The tile on the outside curb facing could have the bottom edge locked in place by the floor tile, in that case it could be the floor tile that is preventing the bottom edge of the curb tile from blowing out. But to me it looks like the curb tile sits on top of the floor tile, so if the bottom of the curb tile wanted to blow out, it would be free to move. Correct? Incorrect?

Based on that assumption? I'd guess that:

3) In the first two photos, it looks like there is a metal track or trim on top of the curb. If that track/trim has been fastened through into the top of the curb, it's possible that moisture is getting to the curb through the fastener holes. The top of the wood curb got wet, then expanded, and it's that expansion that is blowing the curb apart.

I don't know how the membrane was detailed at the curb. It should be wrapped up the inside face, over the top of the curb, and stapled on the outside face of the curb. Any fasteners through the top of the curb could have penetrated the membrane and allow moisture to get to the wood.

I've seen a lot of curbs where the membrane never completely made it over the top of the curb. In that case, it could be as simple as water intrusion through the grout lines on top of the curb.

Again, that's based upon my assumption (cough, cough) that the floor tile outside the shower is not locking the curb tile in place and the bottom edge of the curb tile is free to move if it had to.

Thank you Mongoct,
it seems to me that the floor tile is locking the curb tile in place at the bottom. Therefore only parting on top. The metal piece you see in the picture is from the glass shower enclosure. The glass was installed by the company that sold the shower glass to the contractor and i hope they knew what they were doing. It doesn't show that there were any screws in the metal piece when i open the shower door.
The contractor who did this job sold his business but he agreed to come and have a look at it. We'll see if he actually shows up this weekend.
I assume if it's a moisture problem, which it sure looks like, they would have to redo the whole shower base right?

It depends on the source of the moisture.

Sometimes the glass can be pulled, then the curb can be dismantled from outside the shower and the curb rebuilt. With no wood this time. Then re-assemble and retile, then the glass can be reinstalled.

But if the moisture is coming from underneath...if it's simply moisture vapor, again, the system can be rebuilt as above within reason.

If it's liquid moisture, then that's the wost case. But it doesn't seem to be liquid moisture. Again, if you had water from under the slab coming up and saturating the curb from underneath, you'd likely also have wet grout on the floor around the outside of the shower.

But I'm doing a lot of "supposing". When your guy shows up, take photos. You want to look at the outside of the curb, the layers under the tile. Hopefully you'll find a membrane somewhere in there, which means the membrane was lapped over the top of the curb.

Take a look at Harry Dunbar's curb sandwich for an idea of how a curb can be built. The key is that there are no fasteners through the membrane on the inside face of the curb or on the top of the curb.