i have had rog 1 and never experience this problem had it for years. my rog 3 is less than 2 months old i only press volume button maybe 2 or 3x per WEEK so i didnt notice it untill today. volume down still stucked right now and cannot verify if the service center near me support ROG Phone 3. by the way my area is PHILIPPINES REGION 3
By the way you describe it, it sounds like a hardware related issue best handled by service. Contact your local center and see if they can take a look at your device.