Cracks in hardwood door - what's happened? How to treat?

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Hi - I had a new hardwood door fitted, primed and painted. Within a year the paint started flaking. When I sanded a test area it seems the wood itself has developed cracks - see photos.

Any idea what's happened, and how I should treat it?

https://photos.app.goo.gl/46YoLGe4SfIsgHYz2

Cheers,