Cleaning the switches might help, this includes the volume control which is a simple type of rotary encoder. Contamination of the switches is possible, by dirt (which will clean off easily) or silicone (much harder to remove). Wear can have a similar effect.
I have a Denon system with a digital volume control which is notorious for a similar fault due to the silicone grease they used to give the volume control a nicely damped feel. The lack of surface tension means the grease migrates slowly but steadily until it intermittently insulates the contacts, confusing the algorithms that determine which way you turned the volume
Furniture polish containing silicone can do the same ...
Removing silicone is a challenge ...
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