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IMO, this isn't a good example of 'flare.' It's more of a random scattering of light from its ideal path through the lens. Any multi-element lens design faces this problem, and there is only so much that a practical (affordable!) design can do to combat it. AR coatings help with surface reflections, but even high quality coatings, optimally applied and oriented, reflect one part in several hundred. (In the real world, reflectivity can be one or two percent.) This reflected light bounces off the various surfaces and winds up 'migrating' some distance from its original path, striking the sensor from the wrong direction and in the wrong location. Add to this simple scattering caused by micro-bubbles in the glass, dust particles or a whiff of smoke or sublimated hydrocarbon settling on one of a dozen surfaces, or even a streak of finger oil or pizza grease dripped onto the front element. Got a microfiber cloth? It's full of goop that is just waiting to jump onto the glass.
This is all entirely normal and usually goes undetected.
As usual, our intrepid OP has found a worst-case scene that illustrates the issue quite nicely.