Re: Holbein incompatible with W&N thinner???
I would not be surprised. My Holbein Duos and impasto gel both have issues. The former requires 'extra' mediums, the latter is sticky like rotten chewing gum ... here in Alabama climate ... on alkyd-oil primed surfaces.
The Duos serve well enough for underpaintings and plein air ... where detail and style are not so critical.
But they do not flow as well as my W&N, Old Holland, or RGH oil paints.
Atlelier Interactive acrylics are similar dull muddy trade-offs for extended water miscibility.
Hence, I am forced to keep the palette limited with WMOs and acrylics.