My own view on this is that social services are overwhelmed with the number of trivial (and malicious) reports. It must take time, effort, manpower to simply work out priorities. It presumably cannot be as simple as school reports take priority. So the school did what they are required to do - report (and report again). There are separate reporting lines to education authorities when children are removed from school for home education, moving abroad, not known, etc - but that can be multiple weeks.
On this site the minute a neighbour's child screams, posters exhort reporting to social services or the woefully inept children's charities. And state in naive fake concern that better 1 child be saved than a 100 false reports (or similar). I don't agree - I never have done. Better to identify key risk factors and look at the reporting based on those. So this absolutely awful case has several risk factors even at a surface level: involvement of the (appallingly inept and ongoingly inept) family court, family conflict, prior allegations of abuse, cultural factors (including cultural but also language barriers), school safeguarding reports. There will be other risk factors that we are not aware of. To manage social services' limited resources key risk factors should be prioritised.
As you say poor, poor child. Just dreadful and I personally hold the family court in the highest disgrace.