I have a similar problem as well - see:
My emonPi receives data over USB from a Jeelink USB module, from an emonTx3 and some emonTxShields (all using the Jeelink format radio data).
The emonPi also receives receives measurement data from the atmega328 add-on board - e.g. Vrms and temperature measurements, and LPL format radio data from an emonTx4 via the on-board RFM69.
The emonPi regularly stops recording emonTx4 data from the RFM69, although the measurement data from the atmega328 often continues, so the atmega328 is still working.
I also have an emonBase unit which shows that the transmitted emonTx4 data is not dropping out. The emonBase is next to the emonPi so I don’t think it’s a signal strength issue.
When the emonTx4 data is lost, it disappears from the emonHub log.
At first I thought the the RFM69 was failing, but the problem can be fixed by restarting the emonHub, or halting the emonPi, and turning the power off and back on.
Any thoughts?