Both variations of the h68k has more than enough RAM and storage to run OpenWRT. The specs are way above most commercial routers out there. The issue with your settings not persisting is due to some issue with the TF card/eMMC storage. The OpenWRT squashfs image stores customizations on partition 2 of the mmcblk0 (mmcblk1 if TF card). By default mmcblk0p2 is allocated 400.00 MB shared with other apps so you get about 296 MB for apps, docker images, and customization settings.
*Note: in order to use the remaining capacity of your eMMC or TF you will need to follow [OpenWrt Wiki] Extroot configuration
To solve your issue try re-flashing the latest OpenWRT to a new TF card or eMMC. I have a guide on flashing eMMC without the Rockchip Dev Tools and windows also. LinkStar-H68K-0232 Router Firmware Updates - #36 by AvertEuphemism