Ultegra di2 8050 GS (Medium) Rear Deraileur Battery Drain

Wondering if anyone on here has a solution or idea why the rear mech is causing battery drain. Have exhausted what might be causing it. The mech seems to work fine, shifts into all gears, on the small chainring 34 it doesn't drop in 10 or 11 (which is normal I believe 11 -32), on the large chain ring goes in all gears. Tend to use full synchro in any case.

Have run the pce02 and it's clearly telling me there is a fault with that component regarding battery drain.

The limit screws seem ok, left in various gears and keeps eating the battery at a rate of 10% every 90 mins or so.

Have tried an identical mech and no battery drain issues. The faulty unit has done many miles but apart from the battery drain it's in good condition.

Have cleaned the connection cable area, used electrical solution, but all looks clean.

Not sure if anyone has had a similar issue, perhaps opened up the unit to discover if there is some kind of open/close power circuit fix? Or is there anything else to try?

I've also tried the crash mode recovery and no change. Can't hear any noises when not in use.