Which is why I suggested you had a look at yours ? all that 2mm box and 4mm plate has to end somewhere ?While the old saying "a chain is only as strong as the weakest link" is entirely true, it is the discovery of its location that takes the time.
It would appear to have failed at a point where the forces were/are most concentrated.
As you have fixed that, I would look next at the mating parts to this failure and where they attach for any signs of deformation or stress fractures.
Unless the whole trike is made of that ?