Thank you very much, DjeisonCanuto, for your kind feedback!

As a side note:
With those tests, we can exclude more and more things. Your overall hardware setup seems to work just fine, would be my conclusion, otherwise the problem would show up elsewhere.

The problem is not the image format, another great point to exclude, it is most likely that an image is added at all that triggers it. Which excludes testing more on the image side.
I have also tried to use a Shader in the Hair-material to see if that triggers a problem. Which might not deliver much more insight, but the more data, the easier the tech support to focus.

I will have an eye on the development. Thank you for your very much appreciated patient replies. I'm sure it is annoying to have to deal with this.

Fingers crossed, it will be easily fixed.

Cheers