Nichrome Resistance Wire Globule Formation

Can't see any detail in your circuit diagram. Can you upload it somewhere (e.g. Dropbox) and post a link here?

imo if the wire is defective, it's not the wires fault, it's the quality control, and that must be proven....

With the limited information provided, I don't think you can reasonably narrow this down to defective material being most likely.

In the photo provided with the 'puncture' circled in red, just to the right of the circled area, there appears to be significant corrosion on the wire, as if something detrimental made contact with the Nichrome while it was hot.

The wire needs to be inspected to rule out pitting and other corrosions.

The break also strikes me as particularly jagged for something caused by a material defect which might have increased resistance over a portion of the cross section. The break suggests, to me, an initial crack that resulted in reduced cross section and subsequent localized over heating and failure.

Or the brittle vitreous resistor covering cracked as a result of wire failure and the extreme heat of the arc formed as the conductor with the microscopic inclusion or gas bubble parted...

I find it hard to believe that any MV drive front end would be powered down more than a few times a year for maintenance, except for those nuts who hook those circuits to the production machine E-Stop circuit.

The real question: Was this "defect" present after a long time in place, and functioning normally, or did you just receive this, and it does not function?

Was something massive and edgy dropped on the circuit board?

Makes perfect sense to me. I always seem to choose the lesser of two weevils, when in some cases, the greater of the two is more suitable.

JRaef writes that the life of these resistors is ~8000 cycles & maker is withdrawing support.

comments...

1. This will almost certainly be a short-term rated component.
2. Rate of temperature rise will be much higher than normal rating.
3. Failure will be due stress on rapid heating eventually causing mechanical failure.
4. Failure initiation is localised.
5. You can stop turning drive on so often.
6. Or replace failing resistor with several in series/parallel which have much higher current rating.
7. Higher current rating will mean more resistor metal to reduce temperature rise & stress.
8. "Electric firebar" type able to expand freely might be alternative.
9. Space in drive/temperature may limit replacement options.
10. Brutal approach of fitting well-rated resistors in external housing might be needed if you insist on turning drive on/off a lot.