Glyn - There was another case where reverting back to v2.5 firmware was needed to restore emonTx traffic after an update to v2.6 on an emonPi.
Re: Loss of feeds to EmonPi from EmonTx after update to 2.6
Plus we are still battling against the same issue on the RFM69Pi stops updating/freezes despite following your lead and recompiling the rfm2pi firmware with the updated JeeLib so it maybe you are just experiencing a “good spell” it certainly isn’t fixing it for all unfortunately.