Electroaair issue

After 730 hours I'm having a strange EI issue. The system advances to ~27.5 degrees at 2500 and 3k feet and a bit higher on take-off. The system used to run 23 or so on take-off and low level cruise. If I turn the advance on or off it does not change. It runs around 20 degrees at idle on the ground.

I think I have a direction to go with it but wanted to check with you guys for other suggestions.

More background... This is an older system with the linear advance and the sensor in the right mag hole. Nothing has changed in the system.

Unplug the vacuum advance box, go fly and see if if it stays fixed.