Exorcist? You never know ...
Joe, this is a typical installation ... PoCo service to a new building. Building receives 480/277V 3-phase and has its' own transformers for 208/120v circuits. Power is fed through a main panel, to separate panels that serve the branch circuits. From there, wires go directly to the heat pump. Yes, there are splices along the way, and other 480/277 circuits in the pipe. The other circuits use #10 wire, as compared to the #6 for the heat pump- so it's not likely the wires got mixed up. All circuits have their own 'dedicated' neutral.
The disconnect is your typical 3-phase disconnect. The disconnect was mounted on a pedestal, and had to be moved over a couple inches to allow for filter changing. Both line and load wires were disconnected from the disconnect.
With the breaker OFF, I still read 45-50v on the 'hot' wires. Later, in the course of my work, I managed to get a slight 'tingle' from one of the hots, as well as the undersized neutral.
Now, twh, you have me questioning the transformer hook-ups. Could there be a floating neutral? Well, it won't hurt to check. The transformers are some sort of "extra efficient" type, so it's possible that there's some detail missed in the installation.
