If your AX3000T router has Foresee NAND with bad blocks, and you want to install a Test Build PR #17963 that supports bad block handling, you must first erase the NAND flash via mtk_uartboot:
MT7981> nand erase.force 0x0 0x8000000
Only after you clean up your Foresee NAND from false-positive and real bad blocks (and after restoring erased stock partitions from your own backup), you can install the patched (custom) version of OpenWrt, so that your bad blocks will be properly handled during installation.
See details in the GitHub thread and also see the post from @Lotoss (MAIN PART -> MAIN PART of MAIN PART):
MT7981> tftpboot 0x46000000 BL2.bin
nand write 0x46000000 0x0 0x100000
tftpboot 0x46000000 FIP.bin
nand write 0x46000000 0x380000 0x200000
tftpboot 0x46000000 Nvram.bin
nand write 0x46000000 0x100000 0x40000
tftpboot 0x46000000 Bdata.bin
nand write 0x46000000 0x140000 0x40000
tftpboot 0x46000000 Factory.bin
nand write 0x46000000 0x180000 0x200000
tftpboot 0x46000000 openwrt-mediatek-filogic-xiaomi_mi-router-ax3000t-initramfs-kernel.bin
bootm 0x46000000
Once OpenWrt is loaded in initramfs system mode, install the sysupgrade file openwrt-mediatek-filogic-xiaomi_mi-router-ax3000t-squashfs-sysupgrade.bin via Luci.