Hi belfi814 , welcome to pinside!
If this only happens when scoring double bonus, check this switch on the Double Bonus relay.
For a switch to work 3 things are necessary
1) When open, there should be a small space between the contact points (duh)
2) When closing, the long blade's contact point should push the short blade's contact point enough to move the short blade
3) The contact points should be clean, which they usually will be if #2 is happening