CO2 Sensor DFRobot SEN0219 Problem

Sensor seems to behave as expected for 75 seconds then jumps to an unrealistically high value.

I have applied 5V (from a PowerBank battery) and measured the output voltage using a multimeter - taking readings by hand typically every 5 seconds. The sensor seems to behave as expected for the first 75 seconds then jumps to a higher reading which would seem to be impossible. I have tried it inside and outside over two different days. Every time it seems to go haywire at exactly 75 seconds from power up. I have graphed my readings - both raw voltage output and the converted value to ppm - see below. Atmospheric CO2 should be roughly around 400ppm or slightly less.

Is the sensor faulty?

Hi Scott,

There seems to be a fault in your sensor. Just hit reply to your original order confirmation email and we will get this sorted out for you!