Buy yourself a pack of BVC coils for Nautilus tanks....you might have got a tank leftover from the older stock that came with the BDC coils and not the new BVC ones...there's a huge difference. Those old BDC coils are garbage in my opinion, everyone but one out of the 2 that came with my tank and a five pack of them I bought were horrible and had a problem like you were having, my Nautilus collected dust till the Mini came out and the new BVC style heads that came with it and now my Nautilus is back in my normal rotation and vapes like a champ. the BVC coils still can't do much above 15 watts but as long as you properly prime them they will serve you well....
I am not sure that is the problem but from what you've said so far i'm willing to bet a box of Dunkin' Munchins that I wouldn't be far off from it. To prime the coil you need to drip a little juice around the inside edges of the coil assembly and one drop on each juice port on the sides of the coil assembly, then put it in a full tank of liquid and let it sit and really saturate for a few minutes....you need to do this with the old style BDC coils as well, but those still were a crap shoot even if you did it right...
I am sorry to hear about your problems and wish you the best of luck
