Hi,
I'll send you the export of the field group by email.
This group contained only html fields.
Shorty I had the same issue on a fresh wp install where I created a field group for a setting page with around 15 fields. Then all of a sudden they where gone. Can't remember if I was changing the name of the group but it's likely I did. All of the fields had NO ENTRIES, and slowly slowy I think this problem occurs more likely when there is no data or just html fields..
I'll let you know if the problem occurs again in future.
François