Regrettably some factory firmware will not accept bin files.
Is there a reason why LEDE switched from img to bin?
The extension and the image-format itself are router platform specific and the image contents should match the router's needs. (E.g. ar71xx has factory.img and sysupgrade.bin, while ipq806x has factory.img and sysupgrade.tar images)
Which router you are talking about?
lantiq xway dgn3500b
Installing lede factory bin [1] doesn't work.
Installing openwrt factory img [2] and lede sysupgrade bin [3] works.
[1] https://downloads.lede-project.org/releases/17.01.0/targets/lantiq/xway/lede-17.01.0-r3205-59508e3-lantiq-xway-DGN3500B-squashfs-factory.bin
[2] https://downloads.openwrt.org/chaos_calmer/15.05.1/lantiq/xway/openwrt-15.05.1-lantiq-xway-DGN3500B-squashfs-factory.img
[3] https://downloads.lede-project.org/releases/17.01.0/targets/lantiq/xway/lede-17.01.0-r3205-59508e3-lantiq-xway-DGN3500B-squashfs-sysupgrade.bin
Confirm
upgrade from factory firmware to LEDE factory image is not accepted by router.
The Last working is the last OpenWRT factory-image openwrt-15.05.1-lantiq-xway-DGN3500-squashfs-factory-WW.img