The SMOK OSUB 80w kit comes with the Brit Beast tank and a .4 ohm Baby Q2 coil installed. Your wattage should be fine and, in actuality, can likely go a little higher.
Double check to make sure you are in wattage mode with that coil, as @Bebop suggested. If you are, then make sure you aren't inadvertently bumping the wattage up.
One last thing that could cause it would be a coil that isn't seated properly (or even just a bad coil). If it is moving, even slightly, the ohms can jump all over the place which could result in intermittent hot hits.