Yes - that was helpful @Iso , because now I've realized: this is ONLY affecting the invisible projects.
When I scoll horizontal to the veeeery end (I have a lot of tasks and many invisible because they are closed projects), I can find my "visible" tasks.
@timo, so the bug description is new:
the tasks that are set to "invisible" now will show in the horizontal scrollbar, but are not "visible" but highlighted grey.
Before the last update this horizontal scrollbar was only showing the visible tasks.