And many thousands don't have the issue.
That's an inference. Why do you only magnify one side of the coin? Of the people who responded to this thread, the percentage with the problem is very high. So why not infer there are thousands WITH the issue, instead of without?
The problem is hard to spot on images, unless you stop down to F16 or beyond, which is only a small fraction of photographs. It is only visible to the eye if you closely examine your sensor under appropriate lighting, which only a small percentage of people do. (Some of the people here did not notice until they checked.) Only a small fraction of camera users worldwide visit DPR. And of the ones that visit DPR, only a small fraction post on the MFT forum. Of of the ones that post on the MFT forum, only some read this thread. And only some of those responded.
And with all that, it did not take very long at all to find several people who have an identical issue.
The first time you dig in the sand at the beach and you find a weird animal in a shell with many legs and pincers on the end, you ought not assume you have been especially blessed to find the only crab that has ever lived. It's rational to assume that you are in fact NOT very special, and that what you observe might be quite common.
Since participation in this thread yields a self-selecting sample, it is inappropriate to infer that cameras with the issue comprise either a large or small percentage of cameras worldwide. If it were a very prevalent problem and also very conspicuous, we would have expected to hear more of it. But it's not very conspicuous.
Many people might have the problem and not know it.
But since it took so little time and so little effort with very poor sampling to find several examples, it is very reasonable to believe that this is not a lightning bolt or a meteor strike, an incredibly rare phenomenon. It is more common than that, possibly much more common.
It might be a manufacturing defect that was present on sensors from birth but just not noticed. Or it might be a problem that develops inevitably on those cameras over time. Or it might be something that can happen to any camera, just under conditions so specific it gives the appearance of being random or rare. For example, it could be that it happens to OM-1 sensors if they are exposed to temperatures exceeding 84 degrees Fahrenheit with greater than 72% relative humidity for durations exceeding 3.5 hours, and that if such conditions are achieved, 80% of those sensors will develop the visually detectable problem in 9 to 12 days.
In that example, 80% of cameras have the defect that makes them susceptible to the problem, but it still might seem very rare because of the conditions necessary to provoke it. That would be a problem with high reproducibility once the conditions are known, but low reproducibility if they are not known.
But enough people have reported this in such a short time that it deserves to be taken seriously and not dismissed.