[MLonlooker]

These 2 images look pretty fine to me, though :-)

Generally, long telezoom lenses tend to have bokeh issues.

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FWIW, this is what ChatGPT tells about it ...

"The root cause of a "nisen bokeh" is spherical aberration. Bokeh refers to the aesthetic quality of the out-of-focus areas in a photograph, often highlighted in images with shallow depth of field. Nisen bokeh, sometimes also called "double-lined bokeh" or "ni-sen" (Japanese for "two-line"), occurs when out-of-focus highlights appear as double lines or have a harsh, edgy look instead of smooth, creamy blurs.

Spherical aberration happens when light rays that pass through the edges of a lens are focused at different points than those that pass through the center. This inconsistency causes the out-of-focus highlights to appear with doubled or hard edges, leading to the characteristic look of nisen bokeh.

To minimize spherical aberration and improve bokeh quality, lens manufacturers often use specialized lens elements or designs, such as aspherical elements, to ensure light rays converge more uniformly. This results in smoother and more aesthetically pleasing bokeh in out-of-focus areas of a photograph."

Right thanks, I feel at that I have learnt at least something as to it's cause, and one day when photography equipment has advanced even further down the road to perfection, someone will finally turn their attention to resolving it, or at least reducing it.
 btw, the two images I posted were not to show the effects of nisen bokeh but how I go about reducing it's effects in images ... shooting low..... I'll spare the community the ones that don't look good.