Why do the volume and brightness sliders disappear from Quick Settings?

Why do the volume and brightness sliders suddenly vanish from the Quick Settings panel on Windows 11, leaving only Wi-Fi and Bluetooth buttons? Why do they come back after a restart but disappear again a few hours later?

Is this related to a driver issue, a Windows Update bug, or something with the shell experience? And is there a fix that keeps the sliders visible without rebooting every time?