This seems to be a really specific and peculiar bug, but has been repeatable across different users and on both PC/Mac. In PBIRS September 2019 using Chrome, if a report has so many rows of parameters that it houses a scrollbox, scrolling down in the scroll box causes any parameters that are data driven cascading parameters to do an instant flash and reload and never allow you to select anything. To restate the issue a little more clearly: the parameters work correctly, and then you scroll, and they stop working. This only seems to impact Chrome and not other browsers in our testing.
Here's a video capturing this behavior:
In the above video, you can see that I select a few parameters related to the cascading. I then select and deselect the "Academic Level" parameter 3 times successfully - I can click on and off without any issues. As soon as I scroll the parameter box down and try the same thing again, you can see that the parameter instantly flashes and resets. Nothing else was changed other than scrolling down in the box.
There's obviously local fixes here like reordering parameters or making 3 columns so there's no scroll box, but this is just so strange that I wanted to ensure that it was reported.
Technical notes - we used multiple versions, but here are my specs from the video:
Chrome 80.0.3987.163 (Official Build) (64-bit)
Power BI Report Server September 2019 - Version1.6.7236.4246