I can only only offer some help based on what I know from my QF FF
membership, so I hope this is of some help.
I'm currently a Silver member, and my membership runs from 1st August to 31st July each year. Within that period I must obtain 250 "Status Credits" to maintain (or re-qualify) for my Silver membership, otherwise I drop down to Bronze. I have to continue to achieve 250 Status Credits every year (until I get to something silly like 7000 then I'm a Life Time Silver member).
Status Credits are earned based on the length of flight. I don't know how SQ
determine it, but I would imagine it's something along the same lines. For example LHR
is 60 status credits, where as MEL
is 10. But I can also earn these credits on other One World flights too, so if I fly BA
, I get 20 for a return trip. These all up to my Status Credit total Aug-Jul each year. If I want to become a Gold member (which I do incidentally!), then I must earn 700 status credits between Aug-Jul in the first year and then to re-qualify the following year (and every year thereafter) I need only 600, otherwise I drop back to being a Silver member again. The class you travel also determines the number of credits you get you get the basic in Discount Economy LHR
60 or 360 Credits First Class. There's more rules than this but this is the basic principal.
Hopefully that may be some help, but as "readytotaxi" has already said it almost certainly is to do with your membership year and when you first enrolled.