Not to familiar with later models, but just out of curistory have you checked the plug in connectors on the back of the instrument cluster? Just for the heck of it, I would unplug and reconnect the plug in connector several times and see if it makes any difference in case you have a bad connection somewhere.
Also, have you done a hard reset on the OBC's? if not, disconnect the
negative battery cable and leave it off for about 15 minutes, then reconnect it and see if it helps any.
Good luck!
You could also check the wiring for power and grounds along with the power feed for the lights.
Kinda sounds like you may have a ground problem based on some of your issues?
But being it is much later model than what many of us are familiar with, it could be a BCM (body computer) problem if all the things are controlled through it.
Studying a wiring diagram could provide some insight as to how it is controlled and where it gets its signals from.
I would have thought that a digital mileage display would get its numbers that are stored in the PCM or BCM, so it would not make any difference what instrument cluster head you plug in, it would still show the correct mileage. Now changing the OBC would require reprograming with the current mileage...
Found this picture on line, this is what the back side of the cluster looks like, it shows several connections.
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