With the latest version of Affinity Publisher certain problems with ligatures and character widths were solved. Great job! However, the added logic apparently doesn't apply to numbered lists with text, as used in captions for tables, images or formulae.
The first line in this example is a numbered list with text "Afbeelding <#1>.<tab>". (The word afbeelding is Dutch for image, in case anyone wonders.)
The second line is simply body text with the same font (Calluna Sans).
If I don't use bold style the result is still not good. And I tried the same with Minion Pro as it has the same f_b ligature, but that didn't change a bit.