please deleted this posts
Please provide serial port output of boot loop.
You could try snapshot too - https://firmware-selector.openwrt.org/?version=SNAPSHOT&target=bcm4908%2Fgeneric&id=asus_gt-ac5300.
Thank you for your reply!
I currently don't have a USB-to-TTL serial cable, and I also lack experience in disassembling the device to locate the serial pins, so I'm temporarily unable to provide the serial console output / boot log.
OK, Thank you very much !