So maybe <30 days and cold weather.
I'd say it's likely the screed hadn't thoroughly dried out: simple as that and if so then the floor layer should have advised waiting.
The hollow in your first pic just looks like bad levelling in the screed
I'd say it's likely the screed hadn't thoroughly dried out: simple as that and if so then the floor layer should have advised waiting.
The hollow in your first pic just looks like bad levelling in the screed

