Flange failures are not common, but they are common enough that now Rohloff provides support rings with all new hubs. The rings do not prevent a crack from forming at a spoke hole, but the support rings are intended to support your flange well enough that the wheel will continue to function, allowing a trip to continue if you crack a flange at a spoke hole.
https://www.rohloff.de/en/company/ne...-support-rings

Thus, if you buy a new bike with a new Rohloff hub, the rings should have been built into the wheel without you even hearing about it.

I do not know why some people seem to have multiple flange failures, but a tandem does put a heavy load on a hub. And now that some people are putting Rohloffs on e-bikes, that is an additional stress that the hub was not designed for.

Although they do not recommend adding the rings to a wheel that will continue to be used as is, since I sometimes travel distances far from help, I bought the rings and added them to my hub. I originally built my Rohloff wheel, thus it was an easy task for me to add the rings.

Oops, adding the rings was one more change I made to my Rohloff bike in the past four years, I forgot to mention that.