V10 cordless hoover: diagnose issue with inconsistent start

Hello there,

when  I pull the trigger, I see the charge level but the hoover does not start. It starts inconsistently - sometimes reliably sometimes I need to press a second or a third time. 

I changed the the trigger in the past with a more robust 3D printed one so I feel the trigger is fine. 

I would be be curious to understand the symptoms so I can repair accordingly. 

Thank you,

pierre