I may have mentioned this the last time, but the long-long-press to hard-reboot may require the device to be unplugged. (Since you've mentioned an USBMS session, it's ambiguous whether you tried that with the device sill plugged in or not

).
Also, FWIW, since you've mentioned the charging led: it's somewhat meaningless, because mostly entirely controlled by software (and that mostly form userland, in fact).