I was not able to fix this and I got no support yet from the custom component developer. So I went for the nanoCUL solution (Arduino Nano + CC1101) connected via USB to HA and the Wmbusmeters (W-MBus to MQTT) add-on. This now works fine for me.
The key learning regarding my Sensus IPERL watermeter configuration is that it sends its data every 60 minutes but ONLY if the meter reading changed ! This was initially kind of confusing until I realized how it works.