Turns out to be the FTDI/USB; the only one that will upload sketches is the Wicked Device Nanode so now I’ll try your suggestion of increasing the Rf interval on the emonTx to 10s & see if that helps
That’s what I have - it used to be the stocked “shop” one. The present ‘shop’ one looks to be almost the same, but there are detail differences: the silk screen is different: apart from “OpenEnergyMonitor” replacing “Wicked Devices Nanode”, some component designations have moved and it’s a different font, but the component layout does not appear to have changed.