I was having the same Di2 problems. I deleted the dfly sensor as you did and used the generic sensor detection also. It took a while for the dfly to register while constantly shifting the front shifter back and forth without turning the cranks but once it did detect the dfly everything seemed to be fixed. 40 mile ride today and the Di2 never dropped off line. Thanks for the post regarding the generic sensor detection.
I have been having the same problem with my Di2 set up disappearing after about 5 minutes AND new Bontrager Ion lights randomly doing there own thing and turning off mid-ride - I have installed the new 11.20 firmware and will delete all the sensors and reinstall - I hope that fixes things as it VERY annoying.
Dfly works by radio waves (RF), which can't go through conductive materials. If the bars are aluminum, or conductive CF, the connection is limited to the RF that can leak out through the ends/holes in the bars or be conducted outside via surface waves on the wires. I'd try it outside of the bars.