My Dredd launched two balls for a very funny reason. Would be worth investigating for whoever maintains the Shark Clubs Machines.
My machine was working fine when I installed it, but a few days later, it was launching two balls at a time.
I took the optics off, cleaned them well, and put them back on - same result.
I was flabbergasted.
Then I looked at the ball through. Gee, that looks awful full. Counted the balls in there....
I know I only put six in there. I guess at some point when I hadn't noticed, I had dislodged a stuck ball somewhere on the playfield that had been there for quite some time. Too many balls will cause the launch two ball problem.
In case it helps anyone.