Probably can't access the "new registers" either on a Gen1 hybrid as the firmware hasn't changed.....
Edit - yes that seems to be the issue. You have to tell GivTCP that the Gen1 Hybrid is an AC on old firmware to get the Gen1 Hybrid to communicate. Not sure if that breaks anything else....
Edit2 - incidentally this began happening here at 06:52 30/7/23 so I assume the author of GivTCP pushed out some form of update/patch to GivTCP around then which has broken Gen1 Hybrid comms on D0.450-A0.451 firmware.
Edit3 - looks like telling GivTCP that the Hybrid is an AC on old firmware breaks the Solar forecasting functions which isn't entirely surprising. Ignore that - finger trouble on my end 🙂