I flashed a TP-Link TL-WR1043ND Router and it work's great! - Until i reboot it. After rebooting all Settings are gone and the login screen appears with the message that there is no root password set.
The cause for this is that for one reason or another, the overlay doesn't get mounted, with a tmpfs backed emergency overlay taking its place instead (which is of course lost over a reboot). Why this happens is another question...
It could be that your overlay is (too) small (image too big or previous (saved) settings too large), leaving less than 3 erase blocks (at 64 KB each) for jffs2
or that the jffs2 formatting had not finished before you tried to configure the router
As a first step I'd suggest to invoke "firstboot" again, which resets the overlay again (deleting all configuration), reboot the router and then wait ~5 minutes before accessing the router again; having a look at logread for jffs2 formatting failures could be interesting as well.
sounds wrong. At least for the tl-wr1043 that is an old-style ar71xx/generic router.
For most routers, the only difference between sysupgrade and factory image is just the necessary header & packaging, so that the OEM firmware's flashing routine will accept the Openwrt/LEDE image. For most routers, you can't flash a sysupgrade image using the OEM firmware.
Login to SSH console/terminal and see the output of "df -h". The overlayfs should be mounted as "/".
See exmaple:
Like @slh already explained, if there is not enough free space on the /overlay partition, it may not get mounted, or may get mounted read-only. Then you may have tmpfs mounted for "/", and all settings go just to ramdisk.
You're running an initramfs build, which is intended for testing or flashing the sysupgrade version; not usage. Initramfs stores everything in RAM, it does not have a flash based filesystem.