Thank you @jlazkano, exactly what I needed.
Bootloop after flashing OpenWrt from global firmware v3.xx.xx, follows what you did and it's up and running now.
Links:
MIWIFIRepairTool
http://bigota.miwifi.com/xiaoqiang/tools/MIWIFIRepairTool.x86.zip
MIWIFIRepairTool tutorial
Chinese stock firmware
https://bigota.miwifi.com/xiaoqiang/rom/r4ac/miwifi_r4ac_all_c4b35_2.18.28.bin
https://bigota.miwifi.com/xiaoqiang/rom/r4ac/miwifi_r4ac_firmware_e8a04_2.18.51.bin