Only on Android not on iOs.
I put a slider inside a row layout. I disable runtime the layout. The layout is invisible but the slider (or almost the image of it) is fully visible on the upper left corner of the display.
I notice the same thing since recently. Some elements don’t get hidden anymore but instead, they get their width and height set to zero. This is a problem from many aspects and especially when an element has a border set as the border will still be visible as a dot on the top-left of the screen, indicating the position of the zero-width and height element. This was not the case up until approximately 2 weeks now. In all honesty, I did not even bother raising a bug report as having already done so for numerous other cases and having received close-to-ZERO responses, I just considered it to be a waste of time. I hope someone else gets more lucky than I have so far.
Happens with sliders, rows, and columns. Lots of dots on my screens. 
Eeeeeeexactly!