Can you describe how you determined that the problem is still there with the encoder switch disconnected?? Is this happening spontaneously with no input from the encoder?? From your prior posts I had assumed that this was happening when you were using the push-button.
This sounds very much like a solder whisker or flake intermittently causing connections.? Could be happening anywhere along the path.? For example, an intermittent bridge between pins 6 & 7 or even 6 & 8 (via the mic) could cause this.? The latter of these is interesting - a connection from the mic+ to pin 6 would give an alternate high impedance connection to ground, imitating the switch, and being intermittent based on the sound levels at the mic.? (so the more frustrated you get and the louder you curse the worse the problem gets?)
