Key switch problems afraid to ride it.
The cylinder is attached to a plastic gear, which engages a metal rack that moves with the tilt mechanism. My guess is that there is an issue here and when you turn to ACC, the pieces pop out of place.
The good news... these parts are cheap and very common.
The bad news... they are a total PITA to get to. (Otherwise your mechanic probably would have done a permanent fix.) It manes sense, though. If it were easy to get to these parts, you could easily start the car without a key...
If you are good with this kind of thing, you could probably do the repair over 1-2 days. If you were to pay a mechanic that much time, it would be more cost effective (probably) to get another steering column from a salvage yard and just switch them out.




