As you probably figured the Itaste VV V3.0 isn't designed for RDA/RBAs. Innokin don't give the ohms cut off in their user manual. However using ohms law we can take the known specifications and see why your low ohms aren't working.
The max power of the VV3 is 11w. At top power of 11 watts, a 0.8 ohm coil requires 3.708 amps. This is over the maximum current output of 3.5 amps for the iTaste vv3.
Lets say you have a 1.0 ohm coil and vape at a standard 3.7 volts. This still requires 3.7 amps. So the answer here is that your iTaste isn't capable of the output needed for the low ohms you've tried to use, and cuts off. At 1.2 ohms on 3.7 volts the required amps are 3.083 - within the battery capability but a lot of draw for a small battery. It will drain faster.
Very low ohms are a strain on these small
batteries. It can seem hard waiting, but better to wait until your mech mod arrives and enjoy that.