I'm very surprised to heard that Hakchi 2.30 can soft brick a NES Mini 2018 because with mine, I have had no problem and It works perfectly.
I have fashed the Kernel at first and then synchronized the games two times with only NES supported roms.
Hi
I have bought a Mini NES a few days ago and I have installed Hakchi2 2.30 (not CE).
I have had the message about the unknown checksum but the flash has been successful.
I have only added NES games with the good mappers in order to use the original emulator and not the mods.
It works great...