I am using EX.Bus on LibrePilot (i was actually the one who implemented it in firmware) and I haven't had any issues.
- Did you reboot your board after changing the receiver type in the Hardware configuration page?
- Did you connect the cables to the correct output on the R3, and did you check that the rx and tx was correctly connected to the board?
- Did you use the correct port on the CC3D, only flexi port is supported for EX.Bus?
Regards
/Fredrik