Heater drops temp after 1 hr

New owner of a 2025 XC 90 plug-in. Car has been wonderful on short drives, but frustrating on longer ones- specifically climate control.

I’ll set climate to 72 (outside temp ~50) and things get nice and comfy in the car. After about an hour, the air coming out of the vents gets cold, like AC cold. Bumping the climate up to 80 will force hot air again, so the heat itself works.

Service dept said the system was not giving any error codes, and after ‘testing’ they found nothing wrong. Super frustrating.

Has anyone encountered this issue and successfully gotten their service department to fix it? Any advice?