There are several reasons why your vape device may be producing less vapour than normal, including:
Drained battery
This is the most common reason why your vape device is producing less vapour. Replace it with a fully charged battery.
Device needs priming
Before using your vape device, take a few short draws on the mouthpiece. This will soak the wick in e-liquid and allow your vape device to produce vapour to its full capacity.