Some more information for those who are curious.
We've lost at least 6-7 elements since we switched to lead-free processing mid-year 2021. Before that we didn't have any failures. We've only lost zone 3 elements, so this is a heat-related failure.
We run the final zone at 280*C which is about the minimum we can run while still meeting temperature/time restrictions on the flux we use (that is, time above TAL and time before flux exhaustion).
The attached picture shows the method of failure. Basically the element wires are attached to those copper/brass spacers. The element (nichrome?) wire attaches to the bottom of the screw. The wire always vaporizes between the screw and the element. I'm assuming that what is happening here is that the wire in that area is more likely to get hot because it isn't directly in contact with aluminum. As a result, it can overheat and vaporize.
On the most recent exchange with them, I've suggested that they replace that last piece of wire with a section of copper wire to see if that resolves it. Or, alternatively, move to dual 240V elements such that each would take half the heat and would probably be made out of thicker wire. If the 240V ovens are not failing, then this might be the case - although I'm 99% sure they sent me a 240V element once and it failed as well.