Do you have an RFM12Pi or an RFM69Pi ? It may be that the firmware in the RFM??Pi has been updated to work with an RFM69CW, when you have an RFM12B. I don’t know how or if this happens, but it is the first thing to check.
See Recompiling RFM69Pi firmware - #6 by adpeace
and https://wiki.openenergymonitor.org/index.php/RFM69Pi_V3
If this is the problem, then it looks as if changing the one line in the file firmware.ino
#define RF69_COMPAT 1
to
#define RF69_COMPAT 0
recompiling and reloading to your Pi should work (disclaimer: I’m not an expert on this side.)
I don’t see any reason for that to be the case. The messages are broadcast for any receiver within range to pick up, so two emonPi’s should be able to work together.