This is follow up on this: D-Link Dir-615 rev D4 is not saving my settings
I am facing same problem - power cycle resets all the settings. Downgrading to 17.01.6 solves the problem.
BusyBox v1.28.3 () built-in shell (ash)
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| |.-----.-----.-----.| | | |.----.| |_
| - || _ | -__| || | | || _|| _|
|_______|| __|_____|__|__||________||__| |____|
|__| W I R E L E S S F R E E D O M
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OpenWrt 18.06.1, r7258-5eb055306f
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=== WARNING! =====================================
There is no root password defined on this device!
Use the "passwd" command to set up a new password
in order to prevent unauthorized SSH logins.
--------------------------------------------------
root@OpenWrt:~# df -h
Filesystem Size Used Available Use% Mounted on
/dev/root 2.3M 2.3M 0 100% /rom
tmpfs 13.8M 408.0K 13.4M 3% /tmp
tmpfs 13.8M 56.0K 13.7M 0% /tmp/root
overlayfs:/tmp/root 13.8M 56.0K 13.7M 0% /
tmpfs 512.0K 0 512.0K 0% /dev
root@OpenWrt:~# logread | grep jffs2
Thu Aug 16 07:51:21 2018 kern.notice kernel: [ 0.000000] Kernel command line: console=ttyS0,57600 rootfstype=squashfs,jffs2
Thu Aug 16 07:51:21 2018 kern.info kernel: [ 0.436621] jffs2: version 2.2 (NAND) (SUMMARY) (LZMA) (RTIME) (CMODE_PRIORITY) (c) 2001-2006 Red Hat, Inc.
Thu Aug 16 07:51:21 2018 user.notice kernel: [ 7.642674] mount_root: jffs2 not ready yet, using temporary tmpfs overlay
Thu Aug 16 07:51:34 2018 kern.err kernel: [ 28.849192] jffs2: Too few erase blocks (4)
Thu Aug 16 07:51:34 2018 daemon.err mount_root: failed - mount -t jffs2 /dev/mtdblock6 /rom/overlay: Invalid argument
root@OpenWrt:~# logread | grep -i overlay
Thu Aug 16 07:51:21 2018 user.notice kernel: [ 7.642674] mount_root: jffs2 not ready yet, using temporary tmpfs overlay
Thu Aug 16 07:51:34 2018 daemon.err mount_root: failed - mount -t jffs2 /dev/mtdblock6 /rom/overlay: Invalid argument
root@OpenWrt:~#
I also tried removing some packages to get some free space (i removed all ppp stuff) - but after reboot the packages reappear.