Recently today i got a similar problem, i was just using my galaxy tab(one ui 8.5) and suddenly the quick setting stopped kinda working. When i swiped from anywhere from top it opened notification panel, then i discovered swiping again opened quick setting panel which was very unnatural, so I digged through settings found nothing, and quickstart(goodlock) also nothing, i thought it was a bug so i just changed panel setting to together instead of separate then i would have hanged it back, thinking it would fix it, but i was so mistaken, it made it unusable, quick settings panel was now not opening at all, only the notification shade. I tried opening panel setting from settings, no luck. so i just restarted my tab. thankfully it fixed it, now i changed back to separate and it works like before, i hope that doesnt occur.
And also a lesson i learnt, always backup ur device, because i got so scared that i have to do a reset.....
