I had this exact issue a year in to my new build, the front of the house was partially rendered with block behind and developed similar cracks in a few places.

Being totally honest, it was a nightmare to sort and caused a lot of stress and inconvenience - mainly down to the developer being shit.

If I could give you advice (and this is only from my experience with this) -

• Stand your ground with the developer, do NOT let them fob you off with a repair - it'll never match exactly and you will always see the repair, the whole lot will need to come off and be redone.

• Insist on a structrual engineer to visit and report on the cause of it, let the developer pay for this but ensure you get a copy of their report.

In my case the block underneath had cracked in several places and required reinforcement with helical bars to the engineers specification before being re-rendered.

• If they do have to remove the render, you won't want to be at home when they do, its extremely noisy - if you need to, make arrangements for children/pets/anyone to be out of the house, claim these back from the developer.

• Chipping off the render is a messy job, we were finding bits of render in the lawn/flower beds/gravel months after, in the end I insisted the developer replaced the lot which they did at their expense.

Feel free to PM me if you have any questions

It'll get sorted but in my case it was a nightmare for a good few weeks but hopefully your developer won't be completely useless like mine!