Client advised that post archive excerpts were not displaying Read More link.
I checked and Customizer excerpts length is set to 55 words.
When excerpt is automatic, Read More link displays after the excerpt.
If a short manual excerpt is used (less than 55 words), Read More is missing.
Admittedly, I have not tried a manual excerpt length greater than 55 words.
I advised client to remove manual excerpts for now.