It seems, all CI jobs run tests with --enable-big-digits=30 configure option (i.e. default). Other possible case (=15 bits) is not tested. Maybe there is some build bot, but it's not obvious which one ...
The board features a XL9535 16-bit I/O Expander with I2C Interface. A continuity check confirms all (SCL/SDA/5V/GND) I2C ports share the same bus. The JST PH2.0 4P connector is the same size as ...