Note quite sure about what you have done. Instead of saying ".img" just sspecify the image type, "factory" or "sysupgrade"... (The ending has no real relevance.)
- factory.img image is meant to be used with OEM firmware's flashing routine or the TFTP recovery in the bootloader
- sysupgrade.bin is meant to be used by the OpnWrt sysupgrade routine to sysupgrade to a new OpenWrt version.
Assuming that you have used the correct image, there are some possibilities:
- bad flash block on the kernel area, which causes the rootfs to start from wrong offset. You would likely need a serial connection to debug that. See e.g. discussion near R7800 -> Flashing openwrt causes bootloop (bad block in kernel area) - #13 by anon98444528
(You might overcome that by flashing a smaller image if the block is in late in the kernel area. Ot by using an initramfs image first.)
Having a serial connection and being able to see the boot process would help you a lot in debugging.
Ps. the newest image from week ago works just fine:
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OpenWrt SNAPSHOT, r22387-47de2c6862
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root@router1:~#