I am having issues with my Erx- randomly working/not working and being slow to respond (it's been very wet here) while working fine with the app but not the brifters (which have new batteries in them and the system is fully charged). Would you be able to describe in more detail what you did with the duct tape? Did you wrap a small piece around where it plugs into the mech or ?? I'm not quite sure how to follow your suggestion and I would LOVE to have a working set!
Step 1:
Disconnect the cables from both derailleurs
Step 2:
Be absolutely sure there is no moisture in the cable or port on the derailleurs. Thoroughly inspect with a flashlight, and let it dry overnight if you want to be absolutely sure.
Step 3:
Rear derailleur: create a strip of ductape (2cm x 5cm), connect the cable and wrap it around the derailleur + cable to make a tight fit. Press down on the ductape to ensure no moisture will get in. Make sure the tape surpasses the "cup" (poor design) which fits the cable.
Front derailleur: unmount the whole unit so you have better access to the port. And repeat the process for the FD. This one of more finicky, but just try to make sure you have a reasonable connection. The FD is less likely to ingress water as the port is downward facing, whereas the RD is essentially a convex shape, waiting to pick up rain.
Step 4:
Ride!