Actually hearing the full team radio now of STR and what he said after the race, I don't believe that STR had heat up issues:
lap 4:
Stroll: ---, the tires are struggling, man.
Race Engineer: Yes. Take it easy man, it’s the same for everyone. Tsunoda has DRS but he’s not getting too close. 0.9.
lap 6:
Stroll: This is a shitty pace and my tires are dying.
after the race (formula1.com):
I’d been pushing really hard in those opening laps – the cars around us were definitely faster and the tyres were already struggling.