Problem initialising slider value from code

no, my console is absolutely clean. No errors, no warnings. (and yes they are turned on).

The code is just as that above, but clickableBoxRotHSlider.value stays on its old value while the new value is diffenent. When I cut the first 2 lines and past them unter the other two, then those don't seem to be executed. Thats really weird.

If the cause is the same then the solution will be the same. If it's not then you need to provide more details.

With regard to the solution posted here (in the OP's own Answer) - this is a common pitfall. If the slider already has a callback assigned, then that callback will be called when you set the value through code, and this can lead to complications. You could probably diagnose it with lots of Debug.Logs telling you the value of the slider(s) before and after each assignment, and within the callback function.

Sometimes it can make sense to add the callback function through code, following initialisation, so that it's not invoked on initialisation. In the OP's situation it looks like the two sliders' values are dependent on each other, and it makes sense that that would create a need for more complex logic.

If that doesn't help, you should create a new question, with details of your set-up/code and problem (and link to it from here).

PS I've converted your Answer to comment because Answers are for answers to the question posted, not comments or follow-up questions.