Hi Sue,
I'm thinking I will need a closer look next time if the temperature display flashes again. I've confirmed the heating coil at the bottom (in pics above) does go very hot when I set fridge to have defrost on - but have not set to defrost mode long enough to witness ALL the ice to melt off. I assumed the element was so hot that it would melt the ice ins fast time. But the 2nd time I took the cover off, it seems no frost on the bottom fins - just on the top ; which may mean the same issue you're having with your fridge.
During my last check, I looked at the evaporator. Apparently these Samsung fridges uses 2 heaters. When I test probed the lines, it shows resistance meaning it should function.