Have you disabled the security software on Windows computer?
Otherwise, have you tried using the MiWiFi Repair tool x86 for Windows, provided router is using stock Uboot (not Breed) bootloader:
http://www1.miwifi.com/miwifi_download.html
Some instructions for how to use the tool for another Xiaomi router. Use the tool to install your AC2100 stock image.
https://forum.openwrt.org/t/xiaomi-mi-router-4a-gigabit-edition-r4ag-r4a-gigabit-fully-supported-and-flashable-with-openwrtinvasion/36685/747