You guys are missing the lesson here.

NOBODY can defend these welds.

Even a good looking weld can be problematic.

Obviously in this case as already understood by many a good welder has to balance a fine line between warpage and proper penetration.

Nobody has yet mentioned the fact there was zero weld joint prep, a 45Deg chamfer?

Being a minimal l trained welder does not qualify one to inspect welds definitively, especially ones that they did not weld themselves.

But this is were the wheels come off (pun intended):

In most cases in regular use, nobody needs to spend much time inspecting OEM welds.

This was a weld that is effectively non redundant and risks possible catastrophic outcome in failure.

Our uses are not "regular", our modifications are not OEM tested or designed, therefore anything "we" weld should be suspect, forever.

The OP's welds looked like crap from day one.

They did not wrap around the top of the perch, the highest stressed welded area.

Nobody can convince me the entire welded perch weld failed the second the u bolt was removed.

Most likely it failed slowly over time.

Any weld exposed to the elements that is incrementally failing often shows warning signs, visible cracks, rust stains, etc.

The mistake here is these signs were not spotted.

Why is for the OP (or victim?) to address.

I do my own welds, and I check every one, forever.