I am finding that paragraph styles in Affinity Publisher Mac are prone to 'collect' an unwanted character style, and become corrupted.
Correcting this back on the job and applying 'update style' doesn't work.
The workaround which I have found to work for me is to delete ALL default styles -- groups, para styles, character styles, the lot. And then, starting from scratch and using the dialogue on the left of the text style edit pane, to set the relatively few para styles, each including character/typographic details, that I use in a publication.
As an observation, the Help system details are inadequate. There are many slightly different systems for setting styles, relating paragraph parameters to font parameters, inheritance, shortcuts etc. The Help system information on styles needs to be both clear and comprehensive – for sure users will need to refer to it.