Jan75 There seem to be two types of reflections, the big ones and the small ones around the star itself. I'm pretty sure (after reading all those pre-2017 posts) that the small ones are microlensing off of the sensor.
Actually, I see a grid of the larger halos too. This is your image with the contrast boosted:
For something like that (grid) to happen, the culprit has to also have a repeating structure (a 2D comb transforms into another 2D comb by the Fourier transform). In the case of the large halo, probably reflecting off a piece of class not too far from the sensor (could even be your reducer or flattener, if you are using one.
Try to remove every piece of glass between the objective and the camera (leaving the filter, of course, since you can only see the effect with the filter).
If you are very brave (and can clean the sensor afterwards) you can try to take an image without the anti-reflection glass of the camera to see if the halos go away. Or, try first replicating the above with an artificial star indoors, so at least you won't have a camera without a protection window outdoors, if you can repeat it with an artificial star indoors.
Chen
