[SOLVED]
Many thanks to all the Balena team who helped on this.
The problem turned out to be a corrupted Balena OS on the RPi. Reason unknown.
Reinstalled it for using Envira+ and set up a new app’ from the start and it works fine. See:
https://595cf2a702595d9612abdf74424f88f6.balena-devices.com/d/Af5gRDiRk/enviroplus?orgId=1&refresh=10s&from=1590252696706&to=1590252996706
Now to explore it for the agricultural application we’re planning.
Thanks to all again, and best wishes.