Not sure where and how you got your magnificent misimpression that your diagram vanishes.

Of course it does not: it is one of the 8 tree diagrams of hard bremsstrahlung, e.g. from S M Swanson, Phys Rev 154 (1967) 1601, all related to each other by suitable crossings and permutations of external momenta. They yield the standard O(α³) cross section for the process.

The amp and its line perm brethren are physical indeed. An awful amount of actual experimental physics relies on it, and it has an elegant form, cf. section 3 of Berends & Kleiss. There is no good reason it should vanish.

Not sure where and how you got your magnificent misimpression that your diagram vanishes.

Of course it does not: it is one of the 8 tree diagrams of hard bremsstrahlung, e.g. from S M Swanson, Phys Rev 154 (1967) 1601, all related to each other by suitable crossings and permutations of external momenta. They yield the standard O(α³) cross section for the process.

The amp and its line-perm brethren are physical indeed. An awful amount of actual experimental physics relies on it, and it has an elegant form, cf. section 3 of Berends & Kleiss. There is no good reason it should vanish.