Hi,
That's the same R4AC sku as the two I have here. They come with international version of firmware which uses a different mtd layout (overlay has been doubled in size which moves where OS1 starts).
When you write from the ramfs image it will be writing halfway through overlay.
You need to compile with a matching mtd layout as what the supplied uboot is expecting,
See Xiaomi R4AC - Problems installing OpenWrt - #17 by markky
and
Xiaomi R4AC - Problems installing OpenWrt - #21 by markky
- Mark