Powered brush not working

I have a dyson v8 and suddenly the powered roller brush stopped working. I am also unable to power the smaller brush with this unit. However I happen to have a v10 as well and I can power that brush with the v10 unit.

I checked the voltage output at the connection with a multimeter and got 20.5 to 21 volts when I hit the trigger. I however am unable to get any voltage output reading on the v10 (even though everything works) which is very confusing and frustrating. Is there a reason I can’t measure output voltage on the v10 and it works but can measure output voltage on v8 but it doesn’t?