When the attached SVG file - it's a union flag, source here: http://hjnilsson.github.io/country-flags/ - is opened or placed in Affinity 1.6.7 or the beta 1.7.0.112 , three of the red diagonal elements are invisible. The W3C validator https://validator.w3.org/check is happy with the SVG and it displays elsewhere correctly so this may be Affinity Photo (or it may be me).
Mark
gb.svg