Solved
GA Segments - Not listed in Supermetrics for Google Sheets
Since a couple of weeks I've had some issues with segments that I created in Google Analytics but which were not listed in the sidebar when I creating a query to fetch data.
Sometimes they become only available after a couple of days, some just never seem to appear (or at least too late to be useful)... I figured a delay of a couple of hours might always be possible but a couple of days is really too long.
Thanks for the input.