Mi4c From 5.1 To 7

[Darkmagister]

Hi, I have a mi4c with xiaomi.eu 6.10.27 with Android 5.1, I've just updated with the latest xiaomi.eu with miui9 and Android 7.0, but it doesn't work, just bootloop, so I've flashed back the 6.10.27 but now some Android process crash at boot and make my device unusable so there is a way to make it work again without a factory reset or something like that?
Or I've to use mi flash and do a full reset ?

Please help
Thanks

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