ADC of STM jumping over value's

[MHuyg.1]

So I’m trying to sample 2 analogue signals with the use of DMA. The ADC’s are running on highest possible speeds (core clock). But when I’m looking at the results for some reason one ADC avoid some “lines�? of value’s and instead of giving the right value it remains the previous value. See picture. 

first  samples are from the 1e ADC.(left side)

second 10000 samples are from the 2e ADC. (right side)

[MHuyg.1]

Fergot to mention I'm using STM32F303RE. ADC 1 & 2 but I also have the same problem on other channels and sometimes it switches. Also the value of the white line just changes.

[TDK]

Custom board? Is VREF stable and do you have a decoupling capacitor near the pin?