I have fixed a first problem with USB_HID_SET_REPORT_REQUEST (see USB_HID_SET_REPORT_REQUEST does not work correctly )
I have another issue where after 10 "Set Report" requests (sent from host), kboot stops answering requests.
It looks like there is a credit set at startup and each "Set Report" request consumes a credit. When there is no more credit, no more answers are sent to the host.
Also, trying to program the target using Windows KinetisUpdater, makes the target reboot.
Any fix to these issues ?