Assuming this thread is for real--
Might have been used wood that had been plugged with different wood plugs that dry rotted and fell out like balsam or popular might do.
Also over time said plug glue also could dry and vibration would not help.
Pics, to me, looked to be man made, just too perfectly round.
As an example I once had to repair a cottage that the whole flooring was dropping into the basement.
The 'handyman builder' had used balsam for the floor joists and the owner was heating the humid basement.
All the spruce wood was still just fine. The balsam came away by the handful.
All his flooring held up just fine but I was able to remove the joists with bare hands it was that bad.
Another job that was a sagging floor event was supported by a heavy main beam that looked fine at first.
When I was explaining to the owner what I suspected I rapped the main beam with my hammer and my hammer went clean thru and proved my point.
LOL that owner was thinking that his septic tank was pushed out by the frost since his plumbing would not drain.
Turned out that his whole floor had lowered by about 5 inches. What a repair job that turned out to be.
His crawl space was so humid that moss was growing on most of the wood.
Very unhealthy working under that floor.