I was about to ask could they be flukey too.
Also, you don't say how many there are and what there is for them to go at besides the hay - by which I mean grass. We'd feed commercials on poor/nonexistant grazing hay at the rate of 1 bale per 20 sheep per day, or more if they were not doing well and were cleaning up. If they've got grass then half that much hay.
Sheep need a lot of sugar in the 6-8 weeks before lambing; if not feeding cake at 1lb/head or thereabouts for a commercial type, I'd certainly have a lick out for them - and one that has a high energy content, not just mins and vits. Big sheep growing big twin lambs inside can simply not have enough room to take in enough hay or other forage to glean their dietary requirements in a 24 our period, hence the normal regime of feeding cake in the last 8 weeks of pregnancy, for a mule usually 1/2 to 3/4 lb per head per day from 8 weeks, doubling that in the last 4 weeks. A little less for Texels as there is always a concern about over-large lambs - but if you don't feed twin-bearers enough then they can be short of milk for two.
I have no experience of lambing Suffolks so I don't know how much cake and forage that breed specifically would need, it could be more than I've outlined for our commercials (Texels and Charollais types.)
Other possibilities include minerals/trace elements. Texels need little or no additional copper, but other breeds may need a copper supplement. Also different breeds will need more or less supplementation of vitamins and other elements (cobalt, selenium, etc.)