The SHIFT + TAB command to make the panels and the filmstrip disappear has never worked in Lightroom.
Sometimes only the side panels disappear, but not the filmstrip, and you give the command again, the filmstrip disappears, and the panels come back.
This time it was worse.
I had my images on full screen in grid view, hit shift + tab to get the side panels, and they came, but the images shone through.
I gave the command again, and then the image, that was selected, lost all its 13 virtual copies. Unfortunately, the one ready to print was one of them, and due to my move the back-up system was not ready, and I lost it.
There are still major and truly basic problems with this software. It is all but safe to use. Add stubborn things like long loading times into the develop module, and the Adobe software engineers have their work cut out for more than one upgrade BEFORE they can charge for one.