What could be the reason for these bands in this data acquisition measurement?
The small white bands are from the resolution of the ADC.

The large white bands are most likely from bits that are not there because of manufacturing defects in the ADC's that the DAQ card uses to measure the voltage. They look like this when looking at the ADC's bits vs voltage graph:


Source: https://www.analog.com/en/analog-dialogue/articles/the-right-adc-architecture.html

When the voltage 'lands' on that bit, it actually gets transfer to the bit above or below resulting in an error