I've some experience with GRBL already. The $$ command should return a list of parameters and the corresponding values. The command works in the module and the GRBL returns the values. However, it seems that the message is truncated. I suspect that maybe some buffer limit in the i2c connection or something like that and I wonder if it could be fixed in Core2 side.
The number of chars received correctly is stable (usually the message is truncated at the same place) and there is some random chars at the end.