Never, ever had issues with fastboot rom. Have done install using <fastboot boot twrp.img> process, format storage first and then installing rom which creates persistent twrp install simulating a recovery partition. But decryption of data doesn't always work, as twrp sometimes does not recognize the pattern/password that is assigned when installing the rom during initial configuration. When this occurs, the only thing is to totally wipe everything by doing a complete format and doing a brand new install. This defeats the purpose of an OTA upgrade.The best way to ensure success is:
1. Flash xiaomi.eu rom for fastboot (please use last version).
2. Install TWRP and then flash the rom
This ensures success always
However, when using the fastboot rom, the percentage of your phone into a brick is quite high