I am no gunsmith so this will be a stupid question for some of you, but bear with me please.

Why will cutting 2 inches off a 25 inch barrel change the POI radically at 25 yards. Rifle is open sight and barrel profile is straight and uniform if that makes any sense.

Thank you

cutting it off changes the harmonics. the bullet leaves the barrel at a different point in the vibration cycle.
Changing loads has a similar effect.

2 possibilities occur immediately:

Harmonics/vibration are changed, causing different muzzle whip/barrel time and therefore a different angle of departure

New crown is different angle from original, again causing a different angle of departure. Crown could have been tilted before or tilted now, group size is usually not affected by crown tilt but POI is definitely affected.
Regards, Joe

Another possibility:

If your judging POI from iron sights - Were they moved when the barrel was shortened?

Then there's the velocity thing.

Unless the barrel is straight with no taper, which is unusual on a sporter, the front sight will be several thousandths higher with respect to the rear sight if it was moved back two inches. You don't indicate the amount or where the POI moved to (higher, lower, left, right) which might give additional clues as to the reason.

Very few barrel blanks have a perfectly straight bore. If a barrel is shortened the bore will be found to be eccentric to the exterior (where the iron sights are mounted). Some times the divergence from center can be significant. I have shortened barrels where I had to turn them down slghtly just to get the bore near center before installing the front sight. Regards, Bill.

All very valid points
As mentioned: Harmonics, Crown, Velocity loss, Location of front site VS new location with same front site.
Anyone of these will change your POI.
Most likely it's the combination of the sites and barrel harmonics

It wont change noticably and absolutely not radically at 25 yards.