It seems to be a firmware issue...
I looked at the others Libra 2 we had at home and the one that didn't give me any problems was in an earlier firmware.
I downgraded the Libra 2 which was causing me problems to 4.37.21586 and I reconnected it to Caliber (in version 7.23). I uploaded the same ePub as yesterday and when I disconnected the e-reader, I got the metadata updated !
The book didn't appear immediately on the home page but I found it without problem in the library. I was able to start reading it and it appears on the home page in the started books.
I quickly deactivated WiFi synchronization. Unless Kobo releases a new firmware that corrects this problem, otherwise it will stay in 4.37...
Thank you all for your responses. I wish you a wonderful holiday season!
