This had cost me so much time to solve. I hope it will help someone else. In my case, it seems that the theme creator made some kind of a problem. I am using the Vinova Sport theme.
The problematic strings I had were in the checkout templates, there were also some others in the /layouts and possibly more in other places. I changed their domain, in my case:
from
d='Shop.Theme'
to
d='Shop.Theme.Checkout'
and for some of the other missing strings from
d='Shop.Theme'
to
d='Shop.Theme.Global'
Then I translated them from the back office and it worked.