KamalKPathak , via OnePlus 6 , Sep 26, 2020 : Alert Slider not working properly for Silent option. Recently seeing many people facing the same problem. Specifically for SILENT option.
drl431 , via OnePlus 6 , Sep 26, 2020 : Clean out the groove for the alert slider. Specifically the upper area, as most users keep it in the bottom position, so dirt will build up in the upper area. Use a toothpick or similar probe.
rhyd1am , via OnePlus Community App , Sep 26, 2020 : Clean out the alert slider using a toothpick or something similar to remove any dust or debris that may have built up (even if it looks clean). edit: beaten to it