Many whom have mad blackberry jam wine have reported a stall, while others just ran into the typical slow down as you approach 1.000. If your OG was in 1.090 range there really is no reason why this should not ferment to dry. But there are some questions such as what yeast was used, have you attempted to dose again with nutrient? Many ferments are known to take a while to drop those last 10-20 points, that may simply be the cause. I would give it 10 days and check SG again, if no movement then I would rack it and pitch a new yeast like EC-1118 or K1V-1116, that should take care of it.