Analogous chord created with missing color as the base color is duplicated.
Create new document: Type: web Units: Pixels Color Format: RGB/8 W: 1280 px Height: 800 px DPI: 96
Draw a Rectangle (I made it a square) and fill with base color; then duplicate object 2 times.
Base color: R: 200 G: 35 B: 35 / H: 0 S: 70 L: 46
From Swatches tab: Create palette from document > as application palette
Under Swatches tab: Delete the 2 created fills
From Color tab: Create Color Chord > Analogous
Created palette swatch:
R: 200 G: 35 B: 35 / Shows as H: 0 S: 70 L: 46 2 (duplicated Base color, should be new color 1)
R: 200 G: 118 B: 35 / Shows as H: 0 S: 70 L: 46 (Base color)
R: 200 G: 35 B: 35 / Shows as H: 0 S: 70 L: 46 (new color 2)
I was following this tutorial on YouTube: "Affinity Designer - Colour Chords"
*Notes: possible regression as the person in video creates Analogues palette correctly (I don't know what version they used)
I was able to create all of other 9 palette types correctly from this same video instructions.
My version: 188.8.131.52
Two example files: