I'm not familiar with skip nailing. I did purchase all fasteners and rent the guns at my own expense - the manufacturer wanted nails, they only used staples. I asked them to use nails since that's what the manufacturer wanted, and they agreed if I'd cover rental and nails.

They nailed every 4 - 6 inches, and these guys genuinely seemed to try to do an honest good job. I don't doubt for a second that this problem was unintentional.

Floor buckling 2 1/2 weeks after installation caused by a lack of fasteners ??? That doesn't register. The floor may be loose or creek, but not buckle, that's moisture related. Look forward to seeing pictures.

Although the OP has gone to a great deal of effort to provide as much detail as possible, there is still something missing here. And I cant figure it out. But definitely a moisture issue of some sort (I think). Since Beech is one of the most sensitive woods to moisture changes, im wondering if the heavy rains Winnipeg has had recently might be a factor here; either through elevated humidity in the house, or even water flow under the crawspace slab. Check the grade level around the perimeter of the house, making sure the flow is away from the foundation walls, and that eavetroughs also have runoff pads to divert water from the house.

And send pics!

It has been very rainy, and I agree something doesn't seem to make sense, but one thing I'm quite certain of is the humidity - I've had it under control and monitor it regularly. I was checking it daily for about 2 weeks prior to the install, keeping it right at 45%.

Here are some pictures, sorry to have taken so long to provide them. It's been challenging getting a shot of this, it's something you feel with your foot and is hard to capture in a picture.

These are from one are where it's particularly visible. I feel it all over the floors both on the upper level and lower level - you can just feel the unevenness of the floor height, and when you press down, sure enough, the peak collapses and bottoms out against the subfloor, then bounces back up.

The wood doesn't look cupped to me, which is a good thing. The floor looks "locked in", causing it to buckle.
Here's a theory...Sounds like you have the RH under control. Maybe had a small swing when the installers were working with open doors. A small RH swing with the rain , along with the approx 4% MC difference between the subfloor and the wood, ( within 2% is more desirable ), along with Beech stability. I would check the expansion space, like I mentioned, the floor looks locked in. Sure looks to me like the floor had no where to go, and the points I just mentioned were enough to cause the movement.

Here are some shots of the perimeter of the floor, does this help? The worst section, the one in the photos posted above, is about 3 feet from the wall. The gap is about 1/4". I repeatedly asked the installer about the gap, telling him I'd heard the minimum was 3/4". He insisted that in this area of Canada 1/4" was sufficient. The floor is not pressing on the wall at all though, so I don't think that's the problem.

Still something odd here though. Agreed the floor doesn't looked cupped, but if; as you say, the elevated areas can easily be pushed back down with finger force, The floor cant be under much compression stress either.
I give up, gonna get a job at the gas station.

Sorry I must have been unclear - I have to use my full weight to bounce to push them down (180lbs).

Dang, they turned me down at the gas station.
Ok, during installation, how did they affix the starters and finishing rows? I can clearly see where nail heads were filled, but did they suppliment this with adhesive? And if so, what type?
Since the floor has obviously grown since it was installed, and if the 1/4 inch gap along the walls is the same as when installed, then it is these rows of flooring that are acting as a "false wall".
That still doesn't explain the source of moisture that is the root cause of this problem though.
More investigation into the structure and environment will need to be done to determine this.

Looking at that 1 wall shoots me down. But...l'm, hanging on by a thread...all it takes to be locked in is 2 adjacent or parallel points that are net fit. Is that possible? IMO something had to cause the pressure in order to buckle, with no cupping present.

You can keep your day job Dennis, you may have something there. That floor is definetely locked in. What type of fasteners are top nailed throught those starter boards? That's a good size hole, 16 penny nails ? . I think even if they used a non-flexible adhesive, that pressure would have blown those boards off the adhesive.

Im still leaning toward moisture issues I stated earlier. We're talking a 2nd & 3rd floor. Ofcoarse could be unseen moisture caused by gutters, downspouts, vapor barriers or lack of.

Lack of fasteners (poor nailing schedule and or skip nailing ) and elevated moisture levels can cause that me thinks.

Have the installer pull it up. I wanna see it! If I'm wrong I'll buy some of Howards straps and eat them.

Actually I think if it was a nailing problemo the wood would have filled the expansion space before it buckled,(with all the pressure of the buckle). I think Dennis hit it on the head with the idea of a "wall" may have been created at the starters( the way they were installed). I think that's what may have locked it in, therefor buckle.

But, sounds great, my inventory shows 1263
Hey the way work is right now....I may have to blend some up and see how they taste
Although they are selling pretty good

My first initial thoughts are a conspiracy with you and Dennis against my theory.

But then the typical install guidelines are using an 8d nail to set the row with, so, theoretically that "block" should be insignificant. I feel the next rows must not be fastened to the proper nailing schedule and thus causing the buckle in the floor along with the extra rh in the house from rain..

But if I am wrong, I'd appreciate a little cilantro in the formula of the straps with a nice Chianti to wash it down with.

My only question to Howard is...can I supplement those straps of yours to use with my Crain ratchet straps?