Factory Reset every few days

My TP-Link C2600 does a factory reset every few days (by itself), and I loose all configurations.
And since all log-files are reset as well, it is hard to find the reason.

Does anybody has an idea what could be the issue for this?

I'm running OpenWrt 18.06.1, but I had the issue already with OpenWrt 18.06.0

Normal crash and reboot does not lose the contents of the overlay flash partition.
But if you lose all settings it sounds like you use ramdisk for settings.
Is your flash full? Do you use the official image or a private image with lots of packages?
What does "df -h" say?

I am running the official OpenWrt 18.06.1 image.
Flash should be not full. Actually (as far as I remember) more than 90% available.
Router has 32MB flash storage, and I only installed OpenVPN and ddns.

I do "df -h" when I am back home again.
Router crashed again, all settings gone, and I can not access from remote anymore :frowning:

How do I see if I use ramdisk for settings?
Though, I do not think I do, since I just use the "default installation / setup".

"df -h"

In normal situation, the r/w overlayfs gets mounted on /overlay that is a mtdblock (or ubifs) partition, and only "/tmp" is mounted on tmpfs

root@router2:~# df -h
Filesystem                Size      Used Available Use% Mounted on
/dev/root                 5.5M      5.5M         0 100% /rom
tmpfs                    29.3M    940.0K     28.3M   3% /tmp
/dev/mtdblock5            8.7M    388.0K      8.3M   4% /overlay
overlayfs:/overlay        8.7M    388.0K      8.3M   4% /
tmpfs                   512.0K         0    512.0K   0% /dev

If there is no working /overlay, the overlayfs gets mounted on tmpfs = ramdisk as /tmp/root. Like this:

root@OpenWrt:/# df -h
Filesystem                Size      Used Available Use% Mounted on
rootfs                  124.8M     68.0K    124.7M   0% /
/dev/root                 6.3M      6.3M         0 100% /rom
tmpfs                   124.8M     64.0K    124.8M   0% /tmp
tmpfs                   124.8M     68.0K    124.7M   0% /tmp/root
overlayfs:/tmp/root     124.8M     68.0K    124.7M   0% /

After a boot you will also have log items about that in system log.
Just try e.g. "logread | grep overlay"

the overlayfs mounting looks okay (right?)
but what means the message "overlayfs: upper fs does not support tmpfile" at "logread | grep overlay"?