coils can change resistance + or - by 0.2 ohms.
More drastic changes in resistance might be due to other factors, such as a loose post screw on your
rba, the wire touching something it shouldn't and grounding out, etc.
I've experienced a drop in resistance of 0.5 ohms from a loose post screw. Luckily I never build lower than 0.6 ohms, because 0.0 ohms is a dead short. That can make a battery go into thermal runaway.