If it is the tachograph not recording breaks and not a mistake by yourself then the vehicle should be defected, it should not be on the road and you should not be driving it with a faulty tachograph.
That is of cause if it’s the tachograph that’s at fault 
see at the time it showed i had taken my proper break on the unit plus a few extra mins, wasnt till i got infringements back that it showed i had done 8 and a half hours without a break 
i did get a few others for going like 1 ro 2 mins over the wtd or driving hours