No surprises there.

Different results can come from different muzzle velocities, different shot distances, different impact velocities, different shot placement, different animal body/bone structure etc.

I'm not surprised at all that this bullet can work well on rib shots at long range from the 375H&H.
The 235gn Speer starting out with a muzzle velocity of 2800 fps will only be doing a mere 2000 fps at 300 yards.
That's an 800 fps loss!
Even at 200 yards it will lose 550 fps.
There is always going to be a big difference in that bullets performance when the impact velocities can be so different.

Whack something on the shoulder at under 100 yards with that same 2800 fps mv load and you will most likely have a wounded animal to deal with.

With my 375 H&H 602 Brno, I once shot a half grown sow pig at about 30-40 yards which was running directly away. The 235 gn Speer disintegrated on impact, and created a huge surface wound.
That was enough for me to never trust that bullet loaded to H&H velocities.

Don't get me wrong, I'm not saying it's a bad bullet.
I am saying that, based on my own experience, it is too soft for 375 H&H velocities at shorter distances.

In the lower velocity 375's, including the 375 Whelen and others, it might work just fine.