5 ADc channels to scan within 20us.

Hi I'm currentlz working on STM32G071RB nucleo board to measure five different voltages across a laser within the ON duration of the Laser i.e 20us using DMA. My ADC finishes conversion every 17us(checked using LED in the ADCconcmplt callback). When there is no time constraint(i.e when the laser is always ON) the ADC gives out the correct voltages across 5 nodes but when I try to read the ADC voltages within 20us it appears that the ADC voltages at two nodes are almost halfed. I'm using an exti to trigger the ADC. I collect the ADC smples in the ADCconvcmplt call back and I use a timer of 1s to average the samples collected. Any inputs regarding this is really appreciated. I tried debugging the software but is of no help. kindly help me with your suggestions