I am currently at a loss on what could be happening.
After downloading all faces for OpenSans, I get duplication within the font selection menu in Affinity Designer (see screenshots).
The specific issue comes when I select "semibold" which then causes the faces menu to go blank and and "?" question mark to appear in the fonts menu for OpenSans.
Where is Affinity designer look for its fonts (directories)?
Does Affinity Designer use OpenSans internally?
I think the simple work around is to just install the non-duplicates (it is what I will end up doing if I can't resolve this).
I've tried to do several things, to find the duplicates:
1) Uninstalled OpenSans (the Light, Light Italic, Regular, Italic, Semibold, Bold faces remain)
2) Installing OpenSans again (I get duplicates, but the only one that causes the blank menu is the "SemiBold" face)
3) Disabling OpenSans (same as #1)
4) Searching for the fonts files, Terminal: find / -name "OpenSans*"
5) Checking specific font locations https://support.apple.com/en-us/HT201722
7) Preferences > Clear Fonts