Why won't my rhinestone sorting tray flip everything face up?

Yours is probably fine, the stragglers are usually a static problem, not a tray problem. Cheap acrylic stones build up static like crazy, and the iridescent ones are the worst because of that coating on the back. A few things that helped me: shake side to side in a small circle instead of up and down, keep it gentle, and don't overload it. Like 30 to 40 stones max at a time. If the tray is half full they just slide around togehter and the face down ones never get a chance to catch on the little bumps in the bottom. For the stubborn ones, dry your hands and the tray relly well before you start. Any moisture or skin oils make them stick. Some people wipe the tray with a dryer sheet or just tap it lightly on the table after shaking, that little tap often pops the last few over.

If a bunch are still stuck flat, dump them back in a small zip bag with a pinch of cornstarch or talc, swish it around, and pour them out. Sounds wierd but it kills the static and they flip way easier after that. I only bother doing this for iridescent or AB coated stones now since the plain ones flip fine on thier own.

Also check that your tray actually has the raised dots in the bottom. Some of the cheaper ones are smooth inside and those are basially useless for flipping, they're just a sorting tray. If yours is smooth, that's your dud right there and no amount of shaking will fix it.

The steam thing works for me. On bad static days I do my flipping in the bathroom right after a hot shower, no fan on. The damp air kills the cling almost completly and even the worst AB coated stones flip over in one or two shakes. Way faster than any other fix I tried. Downside is you have to work quick before the air dries out again, but I only need a few minutes for a batch anyway. Try it before you write your tray off.

I'm new here too and mostly use my tray for sorting tiny buttons rather than flipping gems, so I can't speak to the sticking issue, but one thing I noticed with mine is that size seems to matter. The bigger 5mm pieces flip over almost every shake while the tiny 3mm ones just kind of skitter around. Could be the same for yours, maybe sort by size and do the small ones in smaller batches.

Also a question for anyone who knows: does it make a difference if the tray is cold? Mine lives in my craft room near a window and it's definatly worse on chilly mornings, wondering if that's a static thing or just me.

Agreeing with the coating comment, the shiny backed ones were exactly my problem too. What made a difference for me was letting the stones sit in the open bag overnight before a big card session. Fresh out of a sealed pack they cling way worse, prolly all charged up from being rubbed together in there. After airing out a day most of them flip like normal and I only fish out a couple.

Update: tried the bathroom steam trick someone suggested and wow, what a difference. Right after a hot shower with the fan off, even the iridescent ones flip in one or two shakes now. Static was clearly the culprit since they were worst straight from the bag. I also leave a handful out overnight before big sessions like one reply said, and that alone helps a lot. No more picking stragglers out one by one.