Thank you for the comments and testing the firmware. I agree that shift select works better with two hands and FN is too far away from the pointer position. I will test it and merge it later today.
The web tester is coded against the key code in this firmware, so it could be slightly different with other firmware - most importantly it shows keys are registering.
the trackball movement is optimized for the 5 inch screen & resolution. Hope it makes a much more enjoyable - I initially thinking about changing trackball to touchpad, but it seems not necessary now!
Regarding USB power issues, I saw these report - I am sure there is a power brownout issue that triggers QMK going into DFU mode - because the main board is designed for cm3. I tried to reproduce it by plugin all sorts of my common usb devices (thunderbolt nvm, iPhone, usb drives, iPod.. they all seem to be fine for me - via hacker-gadgets usb & usb-c ports) at least I can’t reproduce it for the moments.