The staging version of the site is a clone of the live site so the postmeta didn’t change at all.
I’ve just checked : the data of the tables is exactly the same.
Perhaps there’s a problem with the fact that the 2 sets of tables are stored within one single database, with 2 different prefixes?
It’s like that, I have 2 clones of the same table :
wpstg_postmeta
and
wplive_postmeta