Di2 7971 help...

[Grill]

I'm having a really weird problem with the Di2 on my Plasma 3.
I just replaced the wiring harness for the aero bar and bull horn shifters and everything was working fine, but recently the bar end shifter for the rear mech stopped upshifting. It still downshifts which means the wire hasn't been snipped and I plugged in the other bar end shifter which has the same issue so the issue is not with the shifter itself.
My mechanic is baffled over this as well and I was wondering if anyone else has had this issue or has any suggestions on how to resolve it.

[bmxbandit]

Have you plugged it into the diagnostic kit? I think that will identify the issue. My guess is maybe the upper or lower junction box is to blame.