When I check the device with RS232 serial connection, only I see the question marks after GRUB. I don't see any errors or useful information for troubleshooting.
(character encoding is fine in "SeaBIOS screen v4.15.0.2", "press F10 for changing boot priority" etc. So it's not related with baud rate.)
What have I tried so far?
I did file shasum verification. The image file is OK. I'm decompressing img.gz file with gunzip -k openwrt-xxxxxxxx
I formatted the SD card and filled it with zeros to solve possible data pollution. Then I burned the image again.
I tried booting from USB 2.0 stick instead of SD card.
BIOS reset. I cut the power of the device and took out the BIOS battery for sometime.
I agree, this looks pretty weird. I think it's obviously this specific device related since I could boot it with different PC.
Yes I have a card reader. I can flash old versions and boot without any problems. I guess I need to skip 21.02.2 for now.
Thanks for helping me!
OK I just figured out this. I was trying to boot 21.02.2 generic but on 21.02.1 I was using 64 target not the generic one. So I just need to wait for the 64 (profile?) of 21.02.2 to build. I'm sorry for taking your time.