Well, a couple things to consider. I also added some granular stabilizer about a week ago. My water temp was about 64 at the time. It actually dissolved quite quickly (about 4 hrs) with consistent squeezing and shaking of the tube sock. So perhaps some additional squeezing might help. Ideally in the peak summer months, we look for FC to drop between 2-4 ppm in 24 hours. Colder months it won't drop as fast. When it drops more than that, we look to either algae or lack of CYA. Since your stabilizer hasn't dissolved, that could be one reason why FC is disappearing so fast.
Something else to note - whenever we exceed our recommended FC range based on the current CYA, FC will disappear fast because there's not an adequate amount of CYA for the FC to bond to. That's why many owners who just completed a SLAM see their FC drop rather quickly back to the normal range. Now the cooler water temps will slow this down a bit, but it can still happen. In your case, I would first ensure your stabilizer dissolves, then validate your CYA about a day later. Ensure your CYA reached the target you wanted. Once you validate your CYA, monitor your FC to ensure it remains constant within its range as noted on the Chlorine/CYA Chart. If FC still falls quickly or below the minimum recommended FC level, consider performing an overnight (OCLT) test to rule-out algae.
(They really need an Emoji showing someone bent over the principles desk... 
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