Why do cut potatoes come out hard in the ice. After 1 and 1/2 hours on 450

Was the oven turned on? Calibrated? Use an oven thermometer to check that internal temperature matched the dial on the outside.
And/or consult manufacturer for a service call, under warranty if possible.

Shame no photo was offered.

It's either a problem with your oven (more likely) or the potatoes (less likely) since 1.5 hours is certainly enough time to roast cut potatoes.

But even at 350 °F a whole russet potato should be baked by the 90 minute mark.

Perhaps try a different oven for starters.

I meant oven