Alright, so really there are only two fonts broken, but across 6 templates:
- Modern Business Letter (sans-serif)
- Lush Green
Source Sans Pro:
Noto Sans was a weird one as these fonts are actually installed with LibreOffice. This turned out to be a bug in the templates’ content and styles xmls:
font-family="'Noto Sans Regular'" instead of
font-family="'Noto Sans'" in a couple of places.
I’ve prepared a patch for this to be released in 6.3.0 later this week.
As for Source Sans Pro, the ideal fix for this, as you say, is to package the fonts separately and install them alongside LibreOffice. In the meantime though, I’ve prepared a patch to simply replace the use of Source Sans Pro with Noto Sans in these templates (also to be released in 6.3.0).