A week ago the bias sign was changed of both ETMs. Before this week data are consistent with positive charging for ETMY and negative charging for ETMX. Charging speed is about 10-20[V] per month. 
This week's data for most of quadrants are consistent with the changed sign of charging - negative for ETMY and positive for ETMX. 
Plots are in attachment. 

Note: before measurements ETMX ESD driver was in unusual state: UL, UR, LL was in Hi voltage ON, Hi Volt disconnect OFF, LR was in Hi Voltage OFF, disconnect OFF.
After my measurements I set all quadrants to Hi Voltage ON, Hi voltage disconnect ON.