Power loss after driving over 15km (engine hot)

I have a 2010 Opel corsa D driven under 50k km. The car was parked outside for 5 weeks as I was in vacation (outside temperature -4deg to +6deg). As I came back I found a strange problem every time I drive more than 15-20km.

After stalling the engine after a 15-20km drive, when i start the engine again I’m facing severe power loss. There is absolutely no acceleration as I press the pedal. If I try to move the car front or reverse releasing the clutch slowly there is severe vibration. I checked the coolant- not boiling, coolant level is at right level, radiator fan normal, no check engine light, slight milky white substance under engine oil cap but I guess thats due to condensation. So I pulled over the car and waited like 20mins, engine cooled down and power back, accelerator works normal.

When I drive like 5-6km (normally) I never face this problem. I tried stalling the engine several times in short trips no issue with power.

Is the engine heating up too much? If so what could be the cause? Faulty radiator or the O2 sensor can go inefficient at high temperature?

I checked the temperature of the engine- cold start 12 deg, after 2 km 60 deg, after 5km 80 deg and after 9 km 105 deg. I didn’t stressed the engine more as I’m afraid I might blow the head gasket.

Note: problem only occurs after stalling the engine, I drove for about 40km at a stretch no issues. Once I stall for 5-10 mins and start again, no power.