I removed and installed the app a few times and added and removed the P1 Meter device (2 devices / Stroom & Meterstanden)
I tried installling only 1 of these (Meterstanden) and then the info was shown in Homey, when i added the other (Stroom) the information from the devices were gone. (Both meters were shown in Homey, but without info)
I had to uninstall the devices and the app again and start over.
Once again installing the app and only adding the Meterstanden, the info was shown.
Could you tell me where you put your value codes for the decimal point ?