While I agree that flat, unshaped, cages are behind us my first thought was that this cage may have been "worked with" by a mechanic during the tuning process. Subtle reshaping to control chain movement or rub is pretty common by many wrenches, done well by those who have been around a while.

But your description suggests another possibility. That the first chain derailment might have caused the cage to bend to allow the chain to fit between the cage and the ring. I would check the gap of the outer cage plate as it is above the big ring teeth. 2-3mm is the usual. Also the outer cage plate is usually roughly straight , not bowed.

Front der adjustment and manipulation is far less cut and dried then rear shifting is. If the cage is distorted having some one who has done this stuff many times before might be the better suggestion than a less experienced wrench bending the cage here and there how many number of times...

I'll add, although not asked about, that shifting under power will produce waves of tension and displacement in the chain. This is why when young we were taught to shift under minimal pedal pressure. Andy.