Charlie - Welcome to the forum and to RS ownership!
The R1250RS I test rode had no issues with the quickshifter, which I found to be very similar to my 2016 R1200RS, and there was no sticking up or down.
One thing that I
did find earlier on is that until you get that hand-foot coordination down-pat, there will be a few times when the bike just will not shift up to down without using the clutch, and this may be your problem.
It is very important that when shifting up, the throttle has to be at the very least constant or increasing - the faster the increase the smoother the shift. Likewise, when shifting down, the throttle has to be closed, i.e. you have to be rotating forward. Unlike with shifting up, keeping it constant may not work and the shift lever will seem to be stuck no matter how you press it.
It all makes sense when you think of what a "quick" shifter is designed to do. It is not designed to be used softly / gently, but is designed for aggressive riding and deliberate positive gear changing. Don't treat it like a pseudo-automatic transmission, and it will work well all the time.
Mine has close to 48k on it and is as smooth as anything. I still get the rare skip from 3-N when gearing down with the quick shifter (never with the clutch), but I am not too bothered as I feel that it has something to do with the speed of the downshift and the speed of travel of the bike.
Hope this helps. If that is not what is happening then please do mention it to the BMW tech as they can "re-adapt" the quick shifter electronically, which might help. But I do think it is the coordination thing.