same, also upgrading from 4.1 to 5.1. I am not able to get into rcm too. I think its bricked..
edit: I can get into rmc now, but still getting black screen on boot
edit2: after a while on the black screen, I got a 2021-0003 error which tol dme to hold power button for 12 sec to reboot.
edit3...
it does support 4.1 right? I keep getting 2162-0002 crashing error when I try to boot from hekate into cfw
edit: turns out it was because i didnt have exfat support on the ofw, fixed by following this guide