Thank you for trying to help figure out the problem.
All insert bulbs behave the same at the same time, what is seen in the video is the behavior of al bulbs driven by CN6 and CN7 from the cpu board.
When playing and right after a game (pre attract mode) the lights show this behavior (bright, dim and flickering) when testing is diagnostics the lights are dim all the time but stay on and don't get brighter or dim.

When testing individual lights only that light is on, no other lights come on not even a little.

I was afraid of that...

All of them behave the same at the same time.

Someone told me to replace the bridgerectifier in the backbox becouse the voltage doesn't look steady. He also suggested to replace the "big blue" capacitor. Could a bad capacitor/bridgerectifier really couse this kind of problem?

I'm not sure about the voltage for the controlled lights, where can I measure the 18v for the lampmatrix?

So I disconnected the plugs c6 and c7 on the cpu board. Connected a testwire to pin 1 on c7 and testwire + diode to pin 1 on c6, connected a lamp socket to the testwire's.
The problem was most noticeable on the Star Wars letters so with this set up I tested the lamp for the letter S. The problem stayed the same.... I think the 18v from the power supply is not stable, where do I test this on the psb?
Can't find anything on that subject on pinwiki or other sources.

Thank you for trying to help.

I will try to make a better video. The lights are not powered stable, they flicker and go dim when they shouldn't.
When popbumpers, slingshots or scoops are operated there is no noticeable diverance but when the outhole kicker is operated the lights, especially the "star wars" letters flicker like a campfire.
When I start a game the lights start a little bit dimmer than usual(no flickering) and when the dead star and r2d2 motor start the lights get brighter and a bit of flickering is noticeable.

Thanks in advance.

On my PS the voltage at pin 6/CN4 is between 15v and 16,5v, is this normal or should it be higher ?

I hope someone can confirm...

I noticed that all lights have the same problem but all the letters in "star wars" on the playfield are much more affected..