Since I installed cc2018 I'm having a problem with the palette windows
if I start the palette panel with a html panel button
even if I close the palette panel and then click on an area outside photoshop
and then back in photoshop this reappears
as I could solve this problem.
However, You can use Script UI, Also has a slider interface.
Try to make it a 'dialog' instead of a 'palette'. It was a known bug.