I think my engine is still suffering from a tapper.

The head has been brought away for revision four months/5000 miles ago and new cambelt was fitted.
From start-up (after assembly) it's already been tapping. First I thought the hydraulic lifters were filling itself but after a couple of minutes driving it, it was still tapping. All the lifters and tappets were changed last year so the problem wouldn't lie there.

I think the machine shop and the mechanic both did a good job so I think the problem would be a failure of one of the cambelt parts.
What frustrates me that we used the latest cambelt set and also the waterpump has been changed.
Could the crankpulley or campulley still slip/jump a tooth? And if it slips it would slip all the time doesn't it?

So what I would like to know, what issues can mess up the timing when it was correctly timed at the assembly?

Thanks for the fast respone !

So the timing can only be off during the cambelt assembly?
It can not happen when first starting, running the engine or driving the car?

video of the engine here