I've tried to search this topic, but couldn't quite find it. Although I think it should exist somewhere:
Sometimes (not always) when expanding a stroke, the vector lines change and straight lines bend. Has anyone else had this happen? I've attached an example with before and after. Pay attention to the upper line after expanding the stroke.
It always requires additional touch up to straighten the lines and can get quite annyoing if there are multiple cases of this happening ;)
macOS 10.11.6 (El Capitan)
Affinity Designer 1.5.5