Ohm-jumping with crown tank

I've been having a persistent issue with my crown tank and I'm wondering if anyone else has had this problem too. I run .5 coils and I use the tank with 3 different batteries; an MVP 3.0, a coolfire IV, and an IPV d2. My ohm reading is jumping all over the place, it goes anywhere from .5 to over 1.0 randomly. I use the coolfire most of the time and at first I thought it was a problem with the battery so I sent it back to Innokin for warranty service. I got it back the other day and at first it seemed fine but now its jumping again. Innokin sent a note with my coolfire that said they found the problem and made adjustments to it but while it was out for service I noticed the ohms jumping with my other batteries too. Not AS bad as with the coolfire, but now I'm wondering if the fault lies with the tank/coils. I've changed the coil many times but it doesn't make a difference. This never happened when I used the original iSub tank the coolfire came with and the only reason I bought the crown was because the other coils are rather hard to find. I tested it just now with the other tank and the ohms stayed steady.

Do the coils for this tank just suck? I buy them from reliable shops and they're definitely genuine. I can't imagine that I just have 3 separate faulty batteries. Is there a chance that these coils could actually be harming my batteries?