It is common for HH shifter bolts to work loose over time, unless the holes are drilled to exact fit the shanks.
In your pic from post *1, that long adapter plate; does it have a front support or are the two rear bolts all that is holding it on? At the front, I see what appears to be a second plate. Is that a stabilizer for the long plate?
Or is the long plate a 1-piece plate bolted on at both ends?
IMO without a front anchor, that long plate would eventually work loose.
The bolts that hold the shifter to the plate are a common source of aggravation. I use a grade 12bolt hardware with hardened flatwashers and no lock washers, just a bit of loc-tite. The holes should be a very-tight fit to the shanks; if they are not, they will work loose.