Hmm, we also had a board break a few years back, by someone using CAM350.
They edited the gerbers, (for some reason) and CAM350 decided to re-order the plotting...
That's fine in a simple, stroke-line image, but this plot used LPC voids, and they vanished by virtue of being done too early. Serious PCB errors resulted......
Many PCB tools can disable the fancier gerber options, and this can be a good idea if you want absolute control over the final PCB.
PcbNew could/should consider that too, yes, creates a slightly more verbose file, but you really do know what you will get.
The rendering error the OP shows, does look like an ARC command inside gerbers 'gone wrong'.
An option to remove the ARC simple avoids the issue entirely.