HI there,
Yea, this is a popular application along with the midi one. definitely check out the threads on here for it.
In your case it is NOT unusual for the Reset after programing (flashing) to NOT work. Why is this:
it requires a certain setup on the RTS/CTS as Well as the DSR/DTR Serial ports pins to have it work correctly, think hardware flow control, vs Xon/Xoff software flow control.
sounds like a version build issue. Check the first one and working to the last one. Also are you always using the same Win10 PC? what serial USB vertual port numbers are you reaching?
you may want to clear old connections in the device manager (show hidden devices) and clean house a little.
Are you using a Nordic BLE dongle on the PC?
HTH
GL 
PJ
At a minimum I would include a manual reset initially or a power reset. (usb port with a power switch)
This may be required based on which BSP you use and which Board family (embedded) , (non embed)
Look at the first 2-3 lines of the compiler output and locate what its using, i.e. 2.9.2 or 1.1.8
Check the date of your libraries and use the BSP closest to that 1 ahead and 1 back. see which performs better. WHy would it matter… some BSP handle the interrupts differently and have different priorities.
Be sure you are using a BLE xiao vs, a Sense version.
run the get Chip ID test and see what rev they are also.
REV 2 or REV 3 ?