TRUNK: Corrupted filesystem after sysupgrade on MT7620A

[reinerotto]

Same problem here on MT7621:

Xiaomi Mi Router 4A Gigabit Edition (R4AG/R4A Gigabit) -- fully supported and flashable with OpenWRTInvasion

Looks like some new openwrt-"feature". Have same serious bug on MT7620A. Posted official bug report already, and created some forum message here, too.