Nano pi r5s soft bricked

Hardware Questions and Recommendations
1

Hi all,
i flashed my new nano pi r5s with FriendlyWRT and it worked. After that i did a sysupgrade with a self-compiled OPENWRT-Image and now i can't login to my nano pi. FriendlyWRT had the root-password password.
I tried to reinstall FriendlyWRT but it seems not to boot from SD-Card.
I tried various passwords for root but the nano pi closes the ssh-connection.
How can i install FriendlyWRT again?

2

https://wiki.friendlyelec.com/wiki/index.php/NanoPi_R5S

4.5.3.3 Option 3: Install OS via USB

EDIT: OpenWRT password is blank , meaning root [enter] [enter]