Potential Cause for these Bay Window Cracks in Victorian House in London

I wouldn't call it "normal", unless you're talking about the quality of work to expect in a flipped house. The cracks don't look as much structural as caused by an atrocious job of finishing the corner. It's hard to tell from the posted pictures, but it looks like they ran a corner trowel over the joint without taping it and on top of a couple coats of paint. Between that and likely painting it hurriedly (they didn't really even sand that much), the existing paint separated in the corner. This should be relatively straight-forward to fix - scrape off all the loose material, and then properly tape (I'd use fiberglass), mud and sand the joint.

I find that a urethane caulk works wonders in cases like this. It bonds like no other caulk I've used, can be had in a huge variety of custom colors, doesn't shrink much, remains very flexible, and is paintable. I'm most familiar with OSI Quad.

Be warned, it's extremely sticky--you won't get it off your clothes, and you'll have to wear it off your skin. It cures very slowly, so don't expect it to be skinned over after a few minutes like silicone or latex.

Cut a small opening on the tube and press firmly to inject the caulk deeply into the crack. Use cardboard or a plastic scraper to remove any excess, pressing very firmly to slice the extra caulk off the surface rather than smearing it wide. Ideally you'll be able to apply and tool the caulk in one pass with the tube nozzle, though.